diff --git a/.gitattributes b/.gitattributes
index 90e9754..37df89d 100644
--- a/.gitattributes
+++ b/.gitattributes
@@ -1,7 +1,7 @@
 /.gitattributes export-ignore
 /.github/ export-ignore
 /.gitignore export-ignore
+/demo/ export-ignore
 /phpstan.neon.dist export-ignore
 /phpunit.xml.dist export-ignore
 /tests/ export-ignore
-/demo/ export-ignore
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index d52240d..d2cf7de 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -11,7 +11,7 @@ jobs:
     strategy:
       fail-fast: true
       matrix:
-        php: ['5.3.3', '5.3', '5.4', '5.5', '5.6', '7.0', '7.1', '7.2', '7.3', '7.4', '8.0', '8.1', '8.2', '8.3', '8.4']
+        php: ['8.2', '8.3', '8.4', '8.5']
 
     name: PHP ${{ matrix.php }}
 
@@ -31,15 +31,13 @@ jobs:
 
       - name: Execute PHPCS
         run: |
-          composer require "squizlabs/php_codesniffer=3.13.2"
           ./vendor/bin/phpcs --standard=PSR12 src/ tests/
-        if: ${{ matrix.php == '8.4' }}
+        if: ${{ matrix.php == '8.5' }}
 
       - name: Execute PHPStan
         run: |
-          composer require phpstan/phpstan:2.1.17 phpstan/phpstan-phpunit:2.0.6
           ./vendor/bin/phpstan analyse
-        if: ${{ matrix.php == '8.4' }}
+        if: ${{ matrix.php == '8.5' }}
 
       - name: Execute tests
         run: ./vendor/bin/phpunit
diff --git a/.gitignore b/.gitignore
index 4383716..f40d3d1 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,5 +1,7 @@
-.idea/
-demo/*.jpg
-demo/*.pgm
-demo/temp/
-vendor/
+/.idea/
+/.phpunit.result.cache
+/composer.lock
+/demo/*.jpg
+/demo/*.pgm
+/demo/temp/
+/vendor/
diff --git a/README.md b/README.md
index baef46e..852fd20 100644
--- a/README.md
+++ b/README.md
@@ -92,7 +92,7 @@ You can use these functions :
 * **inline($quality = 80)**, returns the jpeg code directly in the HTML page
 * **setBackgroundColor($r, $g, $b)**, sets the background color to force it (this will disable many effects and is not recommended)
 * **setBackgroundAlpha($alpha)**, sets the background transparency 0 is fully opaque, 127 is fully transparent
-* **setBackgroundImages(array($imagepath1, $imagePath2))**, Sets custom background images to be used as captcha background. It is recommended to disable image effects when passing custom images for background (ignore_all_effects). A random image is selected from the list passed, the full paths to the image files must be passed.
+* **setBackgroundImages([$imagepath1, $imagePath2])**, Sets custom background images to be used as captcha background. It is recommended to disable image effects when passing custom images for background (ignore_all_effects). A random image is selected from the list passed, the full paths to the image files must be passed.
 * **setInterpolation($interpolate)**, enable or disable the interpolation (enabled by default), disabling it will be quicker but the images will look uglier
 * **setIgnoreAllEffects($ignoreAllEffects)**, disable all effects on the captcha image. Recommended to use when passing custom background images for the captcha.
 * **testPhrase($phrase)**, returns true if the given phrase is good
@@ -101,7 +101,7 @@ You can use these functions :
 * **setImageType($type)**, sets the image output type to "jpeg", "png" or "gif"
 * **setScatterEffect($bool)**, enable or disable scatter effect (fuzzyness)
 
-If you want to change the number of character, you can call the phrase builder directly using
+If you want to change the number of characters, you can call the phrase builder directly using
 extra parameters:
 
 ```php
@@ -135,13 +135,13 @@ render a captcha and check it after the submission
 Symfony Bundle
 ================
 
-You can have a look at the following repository to enjoy the Symfony 2 bundle packaging this captcha generator :
+You can have a look at the following repository to enjoy the Symfony 2 bundle packaging this captcha generator:
 https://github.com/Gregwar/CaptchaBundle
 
 Yii2 Extension
 ===============
 
-You can use the following extension for integrating with Yii2 Framework :
+You can use the following extension for integrating with Yii2 Framework:
 https://github.com/juliardi/yii2-captcha
 
 License
diff --git a/composer.json b/composer.json
index a76f5d0..b644f28 100644
--- a/composer.json
+++ b/composer.json
@@ -17,7 +17,7 @@
         }
     ],
     "require": {
-        "php": ">=5.3.0",
+        "php": "^8.2",
         "ext-gd": "*",
         "ext-mbstring": "*",
         "ext-fileinfo": "*",
@@ -29,6 +29,9 @@
         }
     },
     "require-dev": {
-        "phpunit/phpunit": "^4.8.35 || ^5.7.21 || ^6.4 || ^7.0 || ^8.0 || ^9.0"
+        "phpunit/phpunit": "^9.6",
+        "phpstan/phpstan": "2.1.17",
+        "squizlabs/php_codesniffer": "4.0.1",
+        "phpstan/phpstan-phpunit": "2.0.6"
     }
 }
diff --git a/phpstan.neon.dist b/phpstan.neon.dist
index cf79492..94d5454 100644
--- a/phpstan.neon.dist
+++ b/phpstan.neon.dist
@@ -1,9 +1,7 @@
-includes:
-    - ./vendor/phpstan/phpstan-phpunit/extension.neon
-
 parameters:
-    level: 5
-    paths:
-        - src/
-        - tests/
-    treatPhpDocTypesAsCertain: false
+  level: 8
+  reportUnmatchedIgnoredErrors: false
+  paths:
+    - src/
+    - tests/
+  treatPhpDocTypesAsCertain: false
diff --git a/phpunit.xml.dist b/phpunit.xml.dist
index f17e3b4..f5ea52c 100644
--- a/phpunit.xml.dist
+++ b/phpunit.xml.dist
@@ -1,15 +1,13 @@
 <?xml version="1.0" encoding="UTF-8"?>
-
-<phpunit colors="true" bootstrap="vendor/autoload.php">
-    <testsuites>
-        <testsuite name="KnpMenu Test Suite">
-            <directory suffix="Test.php">./tests/</directory>
-        </testsuite>
-    </testsuites>
-
-    <filter>
-        <whitelist>
-            <directory>./src</directory>
-        </whitelist>
-    </filter>
+<phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" colors="true" bootstrap="vendor/autoload.php" xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/9.3/phpunit.xsd">
+  <coverage>
+    <include>
+      <directory>./src</directory>
+    </include>
+  </coverage>
+  <testsuites>
+    <testsuite name="Test Suite">
+      <directory suffix="Test.php">./tests/</directory>
+    </testsuite>
+  </testsuites>
 </phpunit>
diff --git a/src/Gregwar/Captcha/CaptchaBuilder.php b/src/Gregwar/Captcha/CaptchaBuilder.php
index 0d2892d..4337645 100644
--- a/src/Gregwar/Captcha/CaptchaBuilder.php
+++ b/src/Gregwar/Captcha/CaptchaBuilder.php
@@ -1,10 +1,17 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Gregwar\Captcha;
 
-use Exception;
-use InvalidArgumentException;
-use LogicException;
+use GdImage;
+use Gregwar\Captcha\Exception\CaptchaException;
+use Gregwar\Captcha\Exception\InvalidArgumentException;
+use Gregwar\Captcha\Exception\LogicException;
+
+use function imagecolorallocate;
+use function imagettfbbox;
+use function imagettftext;
 
 /**
  * Builds a new captcha image
@@ -15,167 +22,118 @@
  */
 class CaptchaBuilder implements CaptchaBuilderInterface
 {
-    /**
-     * @var array
-     */
-    protected $fingerprint = array();
+    /** Temporary dir, for OCR check */
+    public string $tempDir = '';
 
-    /**
-     * @var bool
-     */
-    protected $useFingerprint = false;
+    /** @var int[] $fingerprint */
+    protected array $fingerprint = [];
 
-    /**
-     * @var array
-     */
-    protected $textColor = array();
+    protected bool $useFingerprint = false;
 
-    /**
-     * @var array
-     */
-    protected $lineColor = null;
+    /** @var array<int, int<0, 255>>|null $textColor */
+    protected ?array $textColor = null;
 
-    /**
-     * @var array
-     */
-    protected $backgroundColor = null;
+    /** @var array<int, int<0, 255>>|null $lineColor */
+    protected ?array $lineColor = null;
 
+    /** @var array<int, int<0, 255>>|null $backgroundColor */
+    protected ?array $backgroundColor = null;
 
-    /**
-     * @var int 0 to 127, 127 is completely transparent
-     */
-    protected $bgAlpha = 0;
+    /** @var int<0, 127> $bgAlpha */
+    protected int $bgAlpha = 0;
 
-    /**
-     * @var array
-     */
-    protected $backgroundImages = array();
+    /** @var string[] $backgroundImages */
+    protected array $backgroundImages = [];
 
-    /**
-     * @var resource|\GdImage
-     */
-    protected $contents = null;
+    protected ?GdImage $contents = null;
 
-    /**
-     * @var string
-     */
-    protected $phrase = null;
+    protected ?string $phrase = null;
 
-    /**
-     * @var PhraseBuilderInterface
-     */
-    protected $builder;
+    protected ?PhraseBuilderInterface $builder = null;
 
-    /**
-     * @var bool
-     */
-    protected $distortion = true;
+    protected bool $distortion = true;
 
     /**
      * The maximum number of lines to draw in front of
      * the image. null - use default algorithm
      */
-    protected $maxFrontLines = null;
+    protected ?int $maxFrontLines = null;
 
     /**
      * The maximum number of lines to draw behind
      * the image. null - use default algorithm
      */
-    protected $maxBehindLines = null;
+    protected ?int $maxBehindLines = null;
 
     /**
      * The maximum angle of char
      */
-    protected $maxAngle = 8;
+    protected int $maxAngle = 8;
 
     /**
      * The maximum offset of char
      */
-    protected $maxOffset = 5;
+    protected int $maxOffset = 5;
 
     /**
-     * Is the interpolation enabled ?
-     *
-     * @var bool
+     * Is the interpolation enabled?
      */
-    protected $interpolation = true;
+    protected bool $interpolation = true;
 
     /**
      * Ignore all effects
-     *
-     * @var bool
      */
-    protected $ignoreAllEffects = false;
+    protected bool $ignoreAllEffects = false;
 
-    /**
-     * @var bool
-     */
-    protected $scatterEffect = true;
+    protected bool $scatterEffect = true;
 
     /**
      * Allowed image types for the background images
      *
-     * @var array
+     * @var string[]
      */
-    protected $allowedBackgroundImageTypes = array('image/png', 'image/jpeg', 'image/gif');
+    protected array $allowedBackgroundImageTypes = ['image/png', 'image/jpeg', 'image/gif'];
 
-    /**
-     * @var string
-     */
-    protected $imageType = "jpeg";
+    protected string $imageType = "jpeg";
+
+    public function __construct(?string $phrase = null, ?PhraseBuilderInterface $builder = null)
+    {
+        $this->builder = (!$builder)
+            ? new PhraseBuilder()
+            : $builder;
+        $this->phrase = is_string($phrase) ? $phrase : $this->builder->build($phrase);
+        $this->tempDir = sys_get_temp_dir() . DIRECTORY_SEPARATOR . 'captcha' . DIRECTORY_SEPARATOR;
+    }
 
     /**
      * The image contents
      */
-    public function getContents()
+    public function getContents(): ?GdImage
     {
         return $this->contents;
     }
 
     /**
      * Enable/Disables the interpolation
-     *
-     * @param $interpolate bool  True to enable, false to disable
-     *
-     * @return CaptchaBuilder
      */
-    public function setInterpolation($interpolate = true)
+    public function setInterpolation(bool $interpolate = true): static
     {
         $this->interpolation = $interpolate;
 
         return $this;
     }
 
-    /**
-     * Temporary dir, for OCR check
-     */
-    public $tempDir = 'temp/';
-
-    /**
-     * @param string|null                 $phrase
-     * @param PhraseBuilderInterface|null $builder
-     */
-    public function __construct($phrase = null, $builder = null)
-    {
-        if ($builder !== null && !$builder instanceof PhraseBuilderInterface) {
-            throw new InvalidArgumentException('Builder ($builder) must implement PhraseBuilderInterface');
-        }
-
-        $this->builder = $builder ?: new PhraseBuilder();
-        $this->phrase = is_string($phrase) ? $phrase : $this->builder->build($phrase);
-    }
-
-    public function setImageType($imageType)
+    public function setImageType(?string $imageType = null): static
     {
         $imageType = is_string($imageType) ? strtolower($imageType) : '';
-        if (in_array($imageType, array('png', 'jpeg', 'gif'))) {
+        if (in_array($imageType, ['png', 'jpeg', 'gif'])) {
             $this->imageType = $imageType;
         }
 
         return $this;
     }
 
-    public function getImageType()
+    public function getImageType(): string
     {
         return $this->imageType;
     }
@@ -183,15 +141,15 @@ public function getImageType()
     /**
      * Setting the phrase
      */
-    public function setPhrase($phrase)
+    public function setPhrase(?string $phrase = null): void
     {
-        $this->phrase = (string) $phrase;
+        $this->phrase = $phrase;
     }
 
     /**
      * Enables/disable distortion
      */
-    public function setDistortion($distortion)
+    public function setDistortion(bool|int $distortion): static
     {
         $this->distortion = (bool) $distortion;
 
@@ -200,42 +158,36 @@ public function setDistortion($distortion)
 
     /**
      * Enables/disable scatter effect - Only applies to PHP 7.4+
-     *
-     * @param bool  $scatterEffect
      */
-    public function setScatterEffect($scatterEffect)
+    public function setScatterEffect(bool $scatterEffect): static
     {
-        if (version_compare(PHP_VERSION, '7.4.0') < 0) {
-            throw new LogicException('Scatter effect is only available on PHP 7.4');
-        }
-
-        $this->scatterEffect = (bool) $scatterEffect;
+        $this->scatterEffect = $scatterEffect;
 
         return $this;
     }
 
-    public function setMaxBehindLines($maxBehindLines)
+    public function setMaxBehindLines(?int $maxBehindLines): static
     {
         $this->maxBehindLines = $maxBehindLines;
 
         return $this;
     }
 
-    public function setMaxFrontLines($maxFrontLines)
+    public function setMaxFrontLines(?int $maxFrontLines): static
     {
         $this->maxFrontLines = $maxFrontLines;
 
         return $this;
     }
 
-    public function setMaxAngle($maxAngle)
+    public function setMaxAngle(int $maxAngle): static
     {
         $this->maxAngle = $maxAngle;
 
         return $this;
     }
 
-    public function setMaxOffset($maxOffset)
+    public function setMaxOffset(int $maxOffset): static
     {
         $this->maxOffset = $maxOffset;
 
@@ -245,7 +197,7 @@ public function setMaxOffset($maxOffset)
     /**
      * Gets the captcha phrase
      */
-    public function getPhrase()
+    public function getPhrase(): ?string
     {
         return $this->phrase;
     }
@@ -253,46 +205,57 @@ public function getPhrase()
     /**
      * Returns true if the given phrase is good
      */
-    public function testPhrase($phrase)
+    public function testPhrase(string $phrase): bool
     {
-        return ($this->builder->niceize($phrase) == $this->builder->niceize($this->getPhrase()));
+        return (
+            $this->getPhrase()
+            && $this->builder
+            && $this->builder->niceize($phrase) == $this->builder->niceize($this->getPhrase()));
     }
 
     /**
      * Instantiation
      */
-    public static function create($phrase = null)
+    public static function create(?string $phrase = null): CaptchaBuilder
     {
         return new self($phrase);
     }
 
     /**
      * Sets the text color to use
+     * @param int<0, 255> $r
+     * @param int<0, 255> $g
+     * @param int<0, 255> $b
      */
-    public function setTextColor($r, $g, $b)
+    public function setTextColor(int $r, int $g, int $b): static
     {
-        $this->textColor = array($r, $g, $b);
+        $this->textColor = [$r, $g, $b];
 
         return $this;
     }
 
     /**
      * Sets the background color to use
+     * @param int<0, 255> $r
+     * @param int<0, 255> $g
+     * @param int<0, 255> $b
      */
-    public function setBackgroundColor($r, $g, $b)
+    public function setBackgroundColor(int $r, int $g, int $b): static
     {
-        $this->backgroundColor = array($r, $g, $b);
+        $this->backgroundColor = [$r, $g, $b];
 
         return $this;
     }
 
     /**
-     * @param  int $alpha 0 to 127, 127 is completely transparent
+     * @param int<0, 127> $alpha 0 to 127, 127 is completely transparent
      * @return $this
+     * @throws InvalidArgumentException
+     * @throws LogicException
      */
-    public function setBackgroundAlpha($alpha)
+    public function setBackgroundAlpha(int $alpha): static
     {
-        if (! is_integer($alpha) || $alpha < 0 || $alpha > 127) {
+        if ($alpha < 0 || $alpha > 127) {
             throw new InvalidArgumentException('Argument $alpha must be an integer between 0 and 127.');
         }
 
@@ -305,28 +268,28 @@ public function setBackgroundAlpha($alpha)
         return $this;
     }
 
-    public function getBackgroundAlpha()
+    public function getBackgroundAlpha(): int
     {
         return $this->bgAlpha;
     }
 
     /**
      * Sets the line color to use
+     * @param int<0, 255> $r
+     * @param int<0, 255> $g
+     * @param int<0, 255> $b
      */
-    public function setLineColor($r, $g, $b)
+    public function setLineColor(int $r, int $g, int $b): static
     {
-        $this->lineColor = array($r, $g, $b);
+        $this->lineColor = [$r, $g, $b];
 
         return $this;
     }
 
     /**
      * Sets the ignoreAllEffects value
-     *
-     * @param  bool $ignoreAllEffects
-     * @return CaptchaBuilder
      */
-    public function setIgnoreAllEffects($ignoreAllEffects)
+    public function setIgnoreAllEffects(bool $ignoreAllEffects): static
     {
         $this->ignoreAllEffects = $ignoreAllEffects;
 
@@ -335,8 +298,9 @@ public function setIgnoreAllEffects($ignoreAllEffects)
 
     /**
      * Sets the list of background images to use (one image is randomly selected)
+     * @param string[] $backgroundImages
      */
-    public function setBackgroundImages(array $backgroundImages)
+    public function setBackgroundImages(array $backgroundImages): static
     {
         $this->backgroundImages = $backgroundImages;
 
@@ -346,16 +310,16 @@ public function setBackgroundImages(array $backgroundImages)
     /**
      * Draw lines over the image
      */
-    protected function drawLine($image, $width, $height, $tcol = null)
+    protected function drawLine(GdImage $image, int $width = 150, int $height = 40, ?int $tcol = null): void
     {
-        if ($this->lineColor === null) {
-            $red = $this->rand(100, 255);
-            $green = $this->rand(100, 255);
-            $blue = $this->rand(100, 255);
-        } else {
+        if ($this->lineColor !== null) {
             $red = $this->lineColor[0];
             $green = $this->lineColor[1];
             $blue = $this->lineColor[2];
+        } else {
+            $red = $this->rand(100, 255);
+            $green = $this->rand(100, 255);
+            $blue = $this->rand(100, 255);
         }
 
         if ($tcol === null) {
@@ -363,24 +327,24 @@ protected function drawLine($image, $width, $height, $tcol = null)
         }
 
         if ($this->rand(0, 1)) { // Horizontal
-            $Xa   = $this->rand(0, $width / 2);
+            $Xa   = $this->rand(0, (int)($width / 2));
             $Ya   = $this->rand(0, $height);
-            $Xb   = $this->rand($width / 2, $width);
+            $Xb   = $this->rand((int)($width / 2), $width);
             $Yb   = $this->rand(0, $height);
         } else { // Vertical
             $Xa   = $this->rand(0, $width);
-            $Ya   = $this->rand(0, $height / 2);
+            $Ya   = $this->rand(0, (int)($height / 2));
             $Xb   = $this->rand(0, $width);
-            $Yb   = $this->rand($height / 2, $height);
+            $Yb   = $this->rand((int)($height / 2), $height);
         }
         imagesetthickness($image, $this->rand(1, 3));
-        imageline($image, $Xa, $Ya, $Xb, $Yb, $tcol);
+        imageline($image, $Xa, $Ya, $Xb, $Yb, (int)$tcol);
     }
 
     /**
      * Apply some post effects
      */
-    protected function postEffect($image, $bg)
+    protected function postEffect(GdImage $image, ?int $bg = null): void
     {
         if (!function_exists('imagefilter')) {
             return;
@@ -395,7 +359,7 @@ protected function postEffect($image, $bg)
         if (defined('IMG_FILTER_SCATTER')) {
             if ($this->scatterEffect && $this->rand(0, 3) != 0 && $bg != null) {
                 $scattered = true;
-                imagefilter($image, IMG_FILTER_SCATTER, 0, 2, array($bg));
+                imagefilter($image, IMG_FILTER_SCATTER, 0, 2, [$bg]);
             }
         }
 
@@ -421,57 +385,78 @@ protected function postEffect($image, $bg)
     /**
      * Writes the phrase on the image
      */
-    protected function writePhrase($image, $phrase, $font, $width, $height)
+    protected function writePhrase(GdImage $image, ?string $phrase, string $font, int $width, int $height): ?int
     {
-        $length = mb_strlen($phrase);
-        if ($length === 0) {
-            return \imagecolorallocate($image, 0, 0, 0);
+        $length = mb_strlen((string)$phrase);
+        if ($length === 0 || !$phrase) {
+            return imagecolorallocate($image, 0, 0, 0) ?: null;
         }
 
         // Gets the text size and start position
         $size = (int) round($width / $length) - $this->rand(0, 3) - 1;
-        $box = \imagettfbbox($size, 0, $font, $phrase);
+        $box = imagettfbbox($size, 0, $font, $phrase);
+        if (!$box) {
+            return null;
+        }
         $textWidth = $box[2] - $box[0];
         $textHeight = $box[1] - $box[7];
         $x = (int) round(($width - $textWidth) / 2);
         $y = (int) round(($height - $textHeight) / 2) + $size;
 
         if (!$this->textColor) {
-            $textColor = array($this->rand(0, 150), $this->rand(0, 150), $this->rand(0, 150));
+            $textColor = [$this->rand(0, 150), $this->rand(0, 150), $this->rand(0, 150)];
         } else {
             $textColor = $this->textColor;
         }
-        $col = \imagecolorallocate($image, $textColor[0], $textColor[1], $textColor[2]);
-
-        // Write the letters one by one, with random angle
-        for ($i = 0; $i < $length; $i++) {
-            $symbol = mb_substr($phrase, $i, 1);
-            $box = \imagettfbbox($size, 0, $font, $symbol);
-            $w = $box[2] - $box[0];
-            $angle = $this->rand(-$this->maxAngle, $this->maxAngle);
-            $offset = $this->rand(-$this->maxOffset, $this->maxOffset);
-            \imagettftext($image, $size, $angle, $x, $y + $offset, $col, $font, $symbol);
-            $x += $w;
+        $col = imagecolorallocate($image, $textColor[0], $textColor[1], $textColor[2]);
+        if ($col !== false) {
+            // Write the letters one by one, with random angle
+            for ($i = 0; $i < $length; $i++) {
+                $symbol = mb_substr($phrase, $i, 1);
+                $box = imagettfbbox($size, 0, $font, $symbol);
+                if (!$box) {
+                    return null;
+                }
+                $w = $box[2] - $box[0];
+                $angle = $this->rand(-$this->maxAngle, $this->maxAngle);
+                $offset = $this->rand(-$this->maxOffset, $this->maxOffset);
+                imagettftext($image, $size, $angle, $x, $y + $offset, $col, $font, $symbol);
+                $x += $w;
+            }
         }
 
-        return $col;
+        return $col ?: null;
     }
 
     /**
      * Try to read the code against an OCR
+     * @throws CaptchaException
      */
-    public function isOCRReadable()
+    public function isOCRReadable(): bool
     {
-        if (!is_dir($this->tempDir)) {
-            @mkdir($this->tempDir, 0755, true);
+        if (!is_dir($this->tempDir) && !mkdir($this->tempDir, 0755, true)) {
+            throw new CaptchaException('Failed to create temporary directory for OCR check: ' . $this->tempDir);
         }
 
         $tempj = $this->tempDir . uniqid('captcha', true) . '.jpg';
         $tempp = $this->tempDir . uniqid('captcha', true) . '.pgm';
 
         $this->save($tempj);
-        shell_exec("convert $tempj $tempp");
-        $value = trim(strtolower(shell_exec("ocrad $tempp")));
+
+        shell_exec("convert " . escapeshellarg($tempj) . " " . escapeshellarg($tempp));
+        if (!file_exists($tempp)) {
+            if (!file_exists($tempj)) {
+                @unlink($tempj);
+            }
+
+            throw new CaptchaException('isOCRReadable failed to convert file for testing.');
+        }
+
+        $ocradOutput = shell_exec("ocrad " . escapeshellarg($tempp));
+        $value = '';
+        if ($ocradOutput) {
+            $value = trim(strtolower($ocradOutput));
+        }
 
         @unlink($tempj);
         @unlink($tempp);
@@ -481,9 +466,15 @@ public function isOCRReadable()
 
     /**
      * Builds while the code is readable against an OCR
-     */
-    public function buildAgainstOCR($width = 150, $height = 40, $font = null, $fingerprint = null)
-    {
+     * @param int[] $fingerprint
+     * @throws CaptchaException
+     */
+    public function buildAgainstOCR(
+        int $width = 150,
+        int $height = 40,
+        ?string $font = null,
+        ?array $fingerprint = null
+    ): void {
         do {
             $this->build($width, $height, $font, $fingerprint);
         } while ($this->isOCRReadable());
@@ -491,14 +482,16 @@ public function buildAgainstOCR($width = 150, $height = 40, $font = null, $finge
 
     /**
      * Generate the image
+     * @param int[] $fingerprint
+     * @throws CaptchaException
      */
-    public function build($width = 150, $height = 40, $font = null, $fingerprint = null)
+    public function build(int $width = 150, int $height = 40, ?string $font = null, ?array $fingerprint = null): static
     {
         if (null !== $fingerprint) {
             $this->fingerprint = $fingerprint;
             $this->useFingerprint = true;
         } else {
-            $this->fingerprint = array();
+            $this->fingerprint = [];
             $this->useFingerprint = false;
         }
 
@@ -506,9 +499,10 @@ public function build($width = 150, $height = 40, $font = null, $fingerprint = n
             $font = __DIR__ . '/Font/captcha' . $this->rand(0, 5) . '.ttf';
         }
 
-        if (empty($this->backgroundImages)) {
+        $bg = 0;
+        if (empty($this->backgroundImages) && $width > 0 && $height > 0) {
             // if background images list is not set, use a color fill as a background
-            $image   = imagecreatetruecolor($width, $height);
+            $image = imagecreatetruecolor($width, $height);
             if ($this->backgroundColor == null) {
                 $bg = imagecolorallocatealpha(
                     $image,
@@ -521,7 +515,8 @@ public function build($width = 150, $height = 40, $font = null, $fingerprint = n
                 $color = $this->backgroundColor;
                 $bg = imagecolorallocatealpha($image, $color[0], $color[1], $color[2], $this->bgAlpha);
             }
-            imagefill($image, 0, 0, $bg);
+
+            imagefill($image, 0, 0, $bg ?: 0);
             imagesavealpha($image, true);
         } else {
             // use a random background image
@@ -531,11 +526,13 @@ public function build($width = 150, $height = 40, $font = null, $fingerprint = n
 
             $image = $this->createBackgroundImageFromType($randomBackgroundImage, $imageType);
         }
-
+        if (!$image) {
+            throw new LogicException('Failed to create background image');
+        }
         // Apply effects
         if (!$this->ignoreAllEffects) {
             $square = $width * $height;
-            $effects = $this->rand($square / 3000, $square / 2000);
+            $effects = $this->rand((int)($square / 3000), (int)($square / 2000));
 
             // set the maximum number of lines to draw in front of the text
             if ($this->maxBehindLines != null && $this->maxBehindLines > 0) {
@@ -555,7 +552,7 @@ public function build($width = 150, $height = 40, $font = null, $fingerprint = n
         // Apply effects
         if (!$this->ignoreAllEffects) {
             $square = $width * $height;
-            $effects = $this->rand($square / 3000, $square / 2000);
+            $effects = $this->rand((int)($square / 3000), (int)($square / 2000));
 
             // set the maximum number of lines to draw in front of the text
             if ($this->maxFrontLines != null && $this->maxFrontLines > 0) {
@@ -570,13 +567,13 @@ public function build($width = 150, $height = 40, $font = null, $fingerprint = n
         }
 
         // Distort the image
-        if ($this->distortion && !$this->ignoreAllEffects) {
-            $image = $this->distort($image, $width, $height, isset($bg) ? $bg : 0);
+        if ($this->distortion && !$this->ignoreAllEffects && $width > 0 && $height > 0) {
+            $image = $this->distort($image, $width, $height, $bg ?: 0);
         }
 
         // Post effects
-        if (!$this->ignoreAllEffects) {
-            $this->postEffect($image, isset($bg) ? $bg : 0);
+        if (!$this->ignoreAllEffects && $image) {
+            $this->postEffect($image, $bg ?: 0);
         }
 
         $this->contents = $image;
@@ -586,8 +583,10 @@ public function build($width = 150, $height = 40, $font = null, $fingerprint = n
 
     /**
      * Distorts the image
+     * @param int<1, max> $width
+     * @param int<1, max> $height
      */
-    public function distort($image, $width, $height, $bg)
+    public function distort(GdImage $image, int $width, int $height, int $bg = 0): ?GdImage
     {
         $contents = imagecreatetruecolor($width, $height);
         imagefill($contents, 0, 0, $bg);
@@ -633,18 +632,22 @@ public function distort($image, $width, $height, $bg)
             }
         }
 
-        return $contents;
+        return $contents ?: null;
     }
 
     /**
      * Saves the Captcha to file
+     * @throws CaptchaException
      */
-    public function save($filename, $quality = 90)
+    public function save(?string $filename = null, int $quality = 90): void
     {
         $imageType = $this->getImageType();
+        if (!$this->contents) {
+            throw new CaptchaException('No image generated');
+        }
         switch ($imageType) {
             case "png":
-                imagepng($this->contents, $filename, $quality / 10); // quality 0-9
+                imagepng($this->contents, $filename, (int)($quality / 10)); // quality 0-9
                 break;
             case "gif":
                 imagegif($this->contents, $filename);
@@ -658,42 +661,45 @@ public function save($filename, $quality = 90)
     /**
      * Gets the image GD
      */
-    public function getGd()
+    public function getGd(): ?GdImage
     {
         return $this->contents;
     }
 
     /**
      * Gets the image contents
+     *
+     * @throws CaptchaException
      */
-    public function get($quality = 90)
+    public function get(int $quality = 90): string
     {
         ob_start();
         $this->output($quality);
 
-        return ob_get_clean();
+        return ob_get_clean() ?: '';
     }
 
     /**
      * Gets the HTML inline base64
      */
-    public function inline($quality = 90)
+    public function inline(int $quality = 90): string
     {
         return sprintf('data:image/%s;base64,%s', $this->getImageType(), base64_encode($this->get($quality)));
     }
 
     /**
      * Outputs the image
+     * @throws CaptchaException
      */
-    public function output($quality = 90)
+    public function output(int $quality = 90): void
     {
         $this->save(null, $quality);
     }
 
     /**
-     * @return array
+     * @return int[]
      */
-    public function getFingerprint()
+    public function getFingerprint(): array
     {
         return $this->fingerprint;
     }
@@ -701,35 +707,26 @@ public function getFingerprint()
     /**
      * Returns a random number or the next number in the
      * fingerprint
+     * @return int<0, 255>
      */
-    protected function rand($min, $max)
+    protected function rand(int $min, int $max): int
     {
-        if (!is_array($this->fingerprint)) {
-            $this->fingerprint = array();
-        }
-
         if ($this->useFingerprint) {
-            $value = current($this->fingerprint);
+            $value = (int)current($this->fingerprint);
+            $value = max(0, $value);
+            $value = min(255, $value);
             next($this->fingerprint);
         } else {
-            $value = mt_rand((int)$min, (int)$max);
+            $value = mt_rand($min, $max);
+            $value = max(0, $value);
+            $value = min(255, $value);
             $this->fingerprint[] = $value;
         }
 
         return $value;
     }
 
-    /**
-     * @param $x
-     * @param $y
-     * @param $nw
-     * @param $ne
-     * @param $sw
-     * @param $se
-     *
-     * @return int
-     */
-    protected function interpolate($x, $y, $nw, $ne, $sw, $se)
+    protected function interpolate(float $x, float $y, int $nw, int $ne, int $sw, int $se): int
     {
         list($r0, $g0, $b0) = $this->getRGB($nw);
         list($r1, $g1, $b1) = $this->getRGB($ne);
@@ -754,14 +751,7 @@ protected function interpolate($x, $y, $nw, $ne, $sw, $se)
         return ($r << 16) | ($g << 8) | $b;
     }
 
-    /**
-     * @param $image
-     * @param $x
-     * @param $y
-     *
-     * @return int
-     */
-    protected function getCol($image, $x, $y, $background)
+    protected function getCol(GdImage $image, float|int $x, float|int $y, int $background): int
     {
         $L = imagesx($image);
         $H = imagesy($image);
@@ -769,31 +759,26 @@ protected function getCol($image, $x, $y, $background)
             return $background;
         }
 
-        return imagecolorat($image, $x, $y);
+        return imagecolorat($image, (int)$x, (int)$y) ?: 0;
     }
 
     /**
-     * @param $col
-     *
-     * @return array
+     * @return array{int, int, int}
      */
-    protected function getRGB($col)
+    protected function getRGB(int $col): array
     {
-        return array(
-            (int) ($col >> 16) & 0xff,
-            (int) ($col >> 8) & 0xff,
-            (int) ($col) & 0xff,
-        );
+        return [
+            ($col >> 16) & 0xff,
+            ($col >> 8) & 0xff,
+            $col & 0xff,
+        ];
     }
 
     /**
      * Validate the background image path. Return the image type if valid
-     *
-     * @param  string $backgroundImage
-     * @return string
-     * @throws Exception
+     * @throws CaptchaException
      */
-    protected function validateBackgroundImage($backgroundImage)
+    protected function validateBackgroundImage(string $backgroundImage): ?string
     {
         // check if file exists
         if (!file_exists($backgroundImage)) {
@@ -802,48 +787,40 @@ protected function validateBackgroundImage($backgroundImage)
                 ? $backgroundImageExploded[count($backgroundImageExploded) - 1]
                 : $backgroundImage;
 
-            throw new Exception('Invalid background image: ' . $imageFileName);
+            throw new CaptchaException('Invalid background image: ' . $imageFileName);
         }
 
         // check image type
-        $finfo = finfo_open(FILEINFO_MIME_TYPE); // return mime type ala mimetype extension
+        $finfo = finfo_open(FILEINFO_MIME_TYPE);
+        if (!$finfo) {
+            throw new CaptchaException('Failed finfo_open');
+        }
+
         $imageType = finfo_file($finfo, $backgroundImage);
         finfo_close($finfo);
 
         if (!in_array($imageType, $this->allowedBackgroundImageTypes)) {
-            throw new Exception(
+            throw new CaptchaException(
                 'Invalid background image type! Allowed types are: '
                     . join(', ', $this->allowedBackgroundImageTypes)
             );
         }
 
-        return $imageType;
+        return $imageType ?: null;
     }
 
     /**
      * Create background image from type
-     *
-     * @param  string $backgroundImage
-     * @param  string $imageType
-     * @return resource|\GdImage
-     * @throws Exception
+     * @throws CaptchaException
      */
-    protected function createBackgroundImageFromType($backgroundImage, $imageType)
+    protected function createBackgroundImageFromType(string $backgroundImage, ?string $imageType = null): GdImage
     {
-        switch ($imageType) {
-            case 'image/jpeg':
-                $image = imagecreatefromjpeg($backgroundImage);
-                break;
-            case 'image/png':
-                $image = imagecreatefrompng($backgroundImage);
-                break;
-            case 'image/gif':
-                $image = imagecreatefromgif($backgroundImage);
-                break;
-
-            default:
-                throw new Exception('Not supported file type for background image!');
-        }
+        $image = match ($imageType) {
+            'image/jpeg' => imagecreatefromjpeg($backgroundImage),
+            'image/png' => imagecreatefrompng($backgroundImage),
+            'image/gif' => imagecreatefromgif($backgroundImage),
+            default => throw new InvalidArgumentException('Not supported file type for background image!'),
+        };
 
         if ($image === false) {
             throw new LogicException('Failed to create background image!');
diff --git a/src/Gregwar/Captcha/CaptchaBuilderInterface.php b/src/Gregwar/Captcha/CaptchaBuilderInterface.php
index bebd070..a7f4661 100644
--- a/src/Gregwar/Captcha/CaptchaBuilderInterface.php
+++ b/src/Gregwar/Captcha/CaptchaBuilderInterface.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Gregwar\Captcha;
 
 /**
@@ -9,21 +11,22 @@ interface CaptchaBuilderInterface
 {
     /**
      * Builds the code
+     * @param int[] $fingerprint
      */
-    public function build($width, $height, $font, $fingerprint);
+    public function build(int $width = 150, int $height = 40, ?string $font = null, ?array $fingerprint = null): static;
 
     /**
      * Saves the code to a file
      */
-    public function save($filename, $quality);
+    public function save(?string $filename = null, int $quality = 90): void;
 
     /**
      * Gets the image contents
      */
-    public function get($quality);
+    public function get(int $quality = 90): string;
 
     /**
      * Outputs the image
      */
-    public function output($quality);
+    public function output(int $quality = 90): void;
 }
diff --git a/src/Gregwar/Captcha/Exception/CaptchaException.php b/src/Gregwar/Captcha/Exception/CaptchaException.php
new file mode 100644
index 0000000..816d8b6
--- /dev/null
+++ b/src/Gregwar/Captcha/Exception/CaptchaException.php
@@ -0,0 +1,12 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Gregwar\Captcha\Exception;
+
+use Exception;
+
+class CaptchaException extends Exception
+{
+    //
+}
diff --git a/src/Gregwar/Captcha/Exception/InvalidArgumentException.php b/src/Gregwar/Captcha/Exception/InvalidArgumentException.php
new file mode 100644
index 0000000..b68b3da
--- /dev/null
+++ b/src/Gregwar/Captcha/Exception/InvalidArgumentException.php
@@ -0,0 +1,10 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Gregwar\Captcha\Exception;
+
+class InvalidArgumentException extends CaptchaException
+{
+    //
+}
diff --git a/src/Gregwar/Captcha/Exception/LogicException.php b/src/Gregwar/Captcha/Exception/LogicException.php
new file mode 100644
index 0000000..a6525ef
--- /dev/null
+++ b/src/Gregwar/Captcha/Exception/LogicException.php
@@ -0,0 +1,10 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Gregwar\Captcha\Exception;
+
+class LogicException extends CaptchaException
+{
+    //
+}
diff --git a/src/Gregwar/Captcha/ImageFileHandler.php b/src/Gregwar/Captcha/ImageFileHandler.php
deleted file mode 100644
index fcd2d9d..0000000
--- a/src/Gregwar/Captcha/ImageFileHandler.php
+++ /dev/null
@@ -1,109 +0,0 @@
-<?php
-
-namespace Gregwar\Captcha;
-
-use Symfony\Component\Finder\Finder;
-
-/**
- * Handles actions related to captcha image files including saving and garbage collection
- *
- * @author Gregwar <g.passault@gmail.com>
- * @author Jeremy Livingston <jeremy@quizzle.com>
- */
-class ImageFileHandler
-{
-    /**
-     * Name of folder for captcha images
-     *
-     * @var string
-     */
-    protected $imageFolder;
-
-    /**
-     * Absolute path to public web folder
-     *
-     * @var string
-     */
-    protected $webPath;
-
-    /**
-     * Frequency of garbage collection in fractions of 1
-     *
-     * @var int
-     */
-    protected $gcFreq;
-
-    /**
-     * Maximum age of images in minutes
-     *
-     * @var int
-     */
-    protected $expiration;
-
-    /**
-     * @param $imageFolder
-     * @param $webPath
-     * @param $gcFreq
-     * @param $expiration
-     */
-    public function __construct($imageFolder, $webPath, $gcFreq, $expiration)
-    {
-        $this->imageFolder      = $imageFolder;
-        $this->webPath          = $webPath;
-        $this->gcFreq           = $gcFreq;
-        $this->expiration       = $expiration;
-    }
-
-    /**
-     * Saves the provided image content as a file
-     *
-     * @param resource|\GdImage $contents
-     *
-     * @return string
-     */
-    public function saveAsFile($contents)
-    {
-        $this->createFolderIfMissing();
-
-        $filename = md5(uniqid()) . '.jpg';
-        $filePath = $this->webPath . '/' . $this->imageFolder . '/' . $filename;
-        imagejpeg($contents, $filePath, 15);
-
-        return '/' . $this->imageFolder . '/' . $filename;
-    }
-
-    /**
-     * Randomly runs garbage collection on the image directory
-     *
-     * @return bool
-     */
-    public function collectGarbage()
-    {
-        if (!mt_rand(1, $this->gcFreq) == 1) {
-            return false;
-        }
-
-        $this->createFolderIfMissing();
-
-        $finder = new Finder();
-        $criteria = sprintf('<= now - %s minutes', $this->expiration);
-        $finder->in($this->webPath . '/' . $this->imageFolder)
-            ->date($criteria);
-
-        foreach ($finder->files() as $file) {
-            unlink($file->getPathname());
-        }
-
-        return true;
-    }
-
-    /**
-     * Creates the folder if it doesn't exist
-     */
-    protected function createFolderIfMissing()
-    {
-        if (!file_exists($this->webPath . '/' . $this->imageFolder)) {
-            mkdir($this->webPath . '/' . $this->imageFolder, 0755);
-        }
-    }
-}
diff --git a/src/Gregwar/Captcha/PhraseBuilder.php b/src/Gregwar/Captcha/PhraseBuilder.php
index 5d79b1c..09be1d4 100644
--- a/src/Gregwar/Captcha/PhraseBuilder.php
+++ b/src/Gregwar/Captcha/PhraseBuilder.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Gregwar\Captcha;
 
 /**
@@ -9,28 +11,17 @@
  */
 class PhraseBuilder implements PhraseBuilderInterface
 {
-    /**
-     * @var int
-     */
-    public $length;
-
-    /**
-     * @var string
-     */
-    public $charset;
-    /**
-     * Constructs a PhraseBuilder with given parameters
-     */
-    public function __construct($length = 5, $charset = 'abcdefghijklmnpqrstuvwxyz123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ')
-    {
-        $this->length = $length;
-        $this->charset = $charset;
+    public function __construct(
+        public int $length = 5,
+        public string $charset = 'abcdefghijklmnpqrstuvwxyz123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ'
+    ) {
+        //
     }
 
     /**
-     * Generates  random phrase of given length with given charset
+     * Generates a random phrase of given length with given charset
      */
-    public function build($length = null, $charset = null)
+    public function build(?int $length = null, ?string $charset = null): string
     {
         if ($length !== null) {
             $this->length = $length;
@@ -52,7 +43,7 @@ public function build($length = null, $charset = null)
     /**
      * "Niceize" a code
      */
-    public function niceize($str)
+    public function niceize(string $str): string
     {
         return self::doNiceize($str);
     }
@@ -60,7 +51,7 @@ public function niceize($str)
     /**
      * A static helper to niceize
      */
-    public static function doNiceize($str)
+    public static function doNiceize(string $str): string
     {
         return strtr(strtolower($str), '01', 'ol');
     }
@@ -68,7 +59,7 @@ public static function doNiceize($str)
     /**
      * A static helper to compare
      */
-    public static function comparePhrases($str1, $str2)
+    public static function comparePhrases(string $str1, string $str2): bool
     {
         return self::doNiceize($str1) === self::doNiceize($str2);
     }
diff --git a/src/Gregwar/Captcha/PhraseBuilderInterface.php b/src/Gregwar/Captcha/PhraseBuilderInterface.php
index 7333b6c..311b7c5 100644
--- a/src/Gregwar/Captcha/PhraseBuilderInterface.php
+++ b/src/Gregwar/Captcha/PhraseBuilderInterface.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace Gregwar\Captcha;
 
 /**
@@ -10,12 +12,12 @@
 interface PhraseBuilderInterface
 {
     /**
-     * Generates  random phrase of given length with given charset
+     * Generates a random phrase of given length with given charset
      */
-    public function build($length = null, $charset = null);
+    public function build(?int $length = null, ?string $charset = null): string;
 
     /**
      * "Niceize" a code
      */
-    public function niceize($str);
+    public function niceize(string $str): string;
 }
diff --git a/tests/CaptchaBuilderTest.php b/tests/Captcha/CaptchaBuilderTest.php
similarity index 66%
rename from tests/CaptchaBuilderTest.php
rename to tests/Captcha/CaptchaBuilderTest.php
index 00be234..f6d8a59 100644
--- a/tests/CaptchaBuilderTest.php
+++ b/tests/Captcha/CaptchaBuilderTest.php
@@ -1,6 +1,6 @@
 <?php
 
-namespace Test;
+namespace Captcha;
 
 use Gregwar\Captcha\CaptchaBuilder;
 use PHPUnit\Framework\TestCase;
@@ -10,22 +10,22 @@ class CaptchaBuilderTest extends TestCase
     /**
      * Captcha phrases
      *
-     * @var array
+     * @var string[]
      */
-    private $phrases = array(
+    private array $phrases = [
         '@!#*?',
         's3cr3t',
         'p4ssw0rd',
         'hello',
         'world'
-    );
+    ];
 
-    public function testCreate()
+    public function testCreate(): void
     {
         $this->assertInstanceOf('Gregwar\Captcha\CaptchaBuilder', CaptchaBuilder::create());
     }
 
-    public function testBuild()
+    public function testBuild(): void
     {
         $this->assertInstanceOf('Gregwar\Captcha\CaptchaBuilder', CaptchaBuilder::create()->build());
 
@@ -35,18 +35,17 @@ public function testBuild()
         }
     }
 
-    public function testDemo()
+    public function testDemo(): void
     {
         $captcha = new CaptchaBuilder();
         $captcha
             ->build()
-            ->save('out.jpg')
-        ;
+            ->save($filename = __DIR__ . '/../generated/out.jpg');
 
-        $this->assertTrue(file_exists(__DIR__ . '/../out.jpg'));
+        $this->assertTrue(file_exists($filename));
     }
 
-    public function testFingerPrint()
+    public function testFingerPrint(): void
     {
         $int = count(CaptchaBuilder::create()
             ->build()
@@ -55,45 +54,44 @@ public function testFingerPrint()
         $this->assertTrue(is_int($int)); // @phpstan-ignore function.alreadyNarrowedType
     }
 
-    public function testImageType()
+    public function testImageType(): void
     {
-        $types = array('jpeg' => IMAGETYPE_JPEG, 'png' => IMAGETYPE_PNG, 'gif' => IMAGETYPE_GIF);
+        $types = [
+            'jpeg' => IMAGETYPE_JPEG,
+            'png' => IMAGETYPE_PNG,
+            'gif' => IMAGETYPE_GIF
+        ];
         foreach ($types as $type => $expected) {
             $captcha = new CaptchaBuilder();
             $captcha->setImageType($type)->build();
 
             // Test save()
-            $captcha->save('out.' . $type);
-            $this->assertType(__DIR__ . '/../out.' . $type, $expected);
+            $captcha->save($filename = __DIR__ . '/../generated/out.' . $type);
+            $this->assertType($filename, $expected);
 
             // Test output()
             ob_start();
             $captcha->output();
-            file_put_contents(__DIR__ . '/../out.' . $type, ob_get_clean());
-            $this->assertType(__DIR__ . '/../out.' . $type, $expected);
+            file_put_contents($filename, ob_get_clean());
+            $this->assertType($filename, $expected);
         }
     }
 
-    public function testImageTransparency()
+    public function testImageTransparency(): void
     {
-        foreach (array(0 => false, 127 => true) as $alpha => $expected) {
+        foreach ([0 => false, 127 => true] as $alpha => $expected) {
             $captcha = new CaptchaBuilder();
             $captcha->setImageType('png')
                 ->setBackgroundColor(0, 0, 0)
                 ->setBackgroundAlpha($alpha)
                 ->build()
-                ->save($filename = __DIR__ . '/out.png');
+                ->save($filename = __DIR__ . '/../generated/out.png');
 
             $this->assertTransparency($filename, $expected);
         }
     }
 
-    /**
-     * @param string $filename
-     * @param bool $expected
-     * @return void
-     */
-    private function assertTransparency($filename, $expected)
+    private function assertTransparency(string $filename, bool $expected): void
     {
         $image = imagecreatefrompng($filename);
         if (!$image) {
@@ -115,17 +113,11 @@ private function assertTransparency($filename, $expected)
                 }
             }
         }
-        imagedestroy($image);
 
         $this->assertSame($expected, $hasTransparency, 'The PNG does not have any transparent pixels.');
     }
 
-    /**
-     * @param string $file
-     * @param int $expected IMAGETYPE_JPEG / IMAGETYPE_PNG / IMAGETYPE_GIF
-     * @return void
-     */
-    private function assertType($file, $expected)
+    private function assertType(string $file, int $expected): void
     {
         $info = getimagesize($file);
         if ($info === false) {
diff --git a/tests/generated/.gitignore b/tests/generated/.gitignore
new file mode 100644
index 0000000..593bcf0
--- /dev/null
+++ b/tests/generated/.gitignore
@@ -0,0 +1,2 @@
+!.gitignore
+*