diff --git a/src/Application/ImageValidator.php b/src/Application/ImageValidator.php
new file mode 100644
index 0000000..ee15c84
--- /dev/null
+++ b/src/Application/ImageValidator.php
@@ -0,0 +1,81 @@
+<?php
+
+declare(strict_types=1);
+
+namespace BattleForge\Application;
+
+final class ImageValidator
+{
+    /**
+     * @return array{string, string} [canonicalMime, extension] for a recognized image, or null.
+     */
+    private static function detect(string $header): ?array
+    {
+        if (substr($header, 0, 8) === "\x89PNG\r\n\x1a\n") {
+            return ['image/png', 'png'];
+        }
+
+        if (substr($header, 0, 3) === "\xff\xd8\xff") {
+            return ['image/jpeg', 'jpg'];
+        }
+
+        if (substr($header, 0, 6) === 'GIF87a' || substr($header, 0, 6) === 'GIF89a') {
+            return ['image/gif', 'gif'];
+        }
+
+        if (substr($header, 0, 4) === 'RIFF' && substr($header, 8, 4) === 'WEBP') {
+            return ['image/webp', 'webp'];
+        }
+
+        return null;
+    }
+
+    public static function validate(
+        string $tempPath,
+        string $declaredMime,
+        int $maxBytes = 2_000_000,
+        int $maxDimension = 512,
+    ): ValidatedImage {
+        if (!is_file($tempPath)) {
+            throw new InvalidImageException('Upload is not a file.');
+        }
+
+        $size = filesize($tempPath);
+        if ($size === false || $size > $maxBytes) {
+            throw new InvalidImageException("File exceeds the {$maxBytes} byte limit.");
+        }
+
+        $handle = fopen($tempPath, 'rb');
+        if ($handle === false) {
+            throw new InvalidImageException('Could not read upload.');
+        }
+        $header = fread($handle, 12);
+        fclose($handle);
+        if ($header === false || strlen($header) < 12) {
+            throw new InvalidImageException('Upload is too small to be an image.');
+        }
+
+        $detected = self::detect($header);
+        if ($detected === null) {
+            throw new InvalidImageException('File is not a supported image type.');
+        }
+
+        [$canonical, $extension] = $detected;
+
+        if ($declaredMime !== $canonical) {
+            throw new InvalidImageException('Declared MIME does not match file contents.');
+        }
+
+        $info = getimagesize($tempPath);
+        if ($info === false) {
+            throw new InvalidImageException('Image is corrupt or unreadable.');
+        }
+
+        [$width, $height] = $info;
+        if ($width > $maxDimension || $height > $maxDimension) {
+            throw new InvalidImageException("Image dimensions exceed the {$maxDimension} pixel limit.");
+        }
+
+        return new ValidatedImage($canonical, $extension);
+    }
+}
diff --git a/src/Application/InvalidImageException.php b/src/Application/InvalidImageException.php
new file mode 100644
index 0000000..5880d6b
--- /dev/null
+++ b/src/Application/InvalidImageException.php
@@ -0,0 +1,11 @@
+<?php
+
+declare(strict_types=1);
+
+namespace BattleForge\Application;
+
+use RuntimeException;
+
+final class InvalidImageException extends RuntimeException
+{
+}
diff --git a/src/Application/ValidatedImage.php b/src/Application/ValidatedImage.php
new file mode 100644
index 0000000..5a9431f
--- /dev/null
+++ b/src/Application/ValidatedImage.php
@@ -0,0 +1,14 @@
+<?php
+
+declare(strict_types=1);
+
+namespace BattleForge\Application;
+
+final readonly class ValidatedImage
+{
+    public function __construct(
+        public string $canonicalMime,
+        public string $extension,
+    ) {
+    }
+}
diff --git a/tests/Unit/Application/ImageValidatorTest.php b/tests/Unit/Application/ImageValidatorTest.php
new file mode 100644
index 0000000..422a378
--- /dev/null
+++ b/tests/Unit/Application/ImageValidatorTest.php
@@ -0,0 +1,180 @@
+<?php
+
+declare(strict_types=1);
+
+namespace BattleForge\Tests\Unit\Application;
+
+use BattleForge\Application\ImageValidator;
+use BattleForge\Application\InvalidImageException;
+use PHPUnit\Framework\Attributes\DataProvider;
+use PHPUnit\Framework\TestCase;
+
+final class ImageValidatorTest extends TestCase
+{
+    private const TMP_DIR = '/tmp';
+
+    public function testItAcceptsAValidPng(): void
+    {
+        $path = self::TMP_DIR . '/bf-valid-' . bin2hex(random_bytes(4)) . '.png';
+        self::assertNotFalse(file_put_contents($path, self::validPng(8, 8)));
+
+        try {
+            $result = ImageValidator::validate($path, 'image/png');
+            self::assertSame('image/png', $result->canonicalMime);
+            self::assertSame('png', $result->extension);
+        } finally {
+            unlink($path);
+        }
+    }
+
+    public function testItRejectsAFileWithTheWrongDeclaredMime(): void
+    {
+        $path = self::TMP_DIR . '/bf-bad-mime-' . bin2hex(random_bytes(4)) . '.png';
+        self::assertNotFalse(file_put_contents($path, self::validPng(8, 8)));
+
+        try {
+            $this->expectException(InvalidImageException::class);
+            $this->expectExceptionMessage('Declared MIME does not match file contents');
+            ImageValidator::validate($path, 'image/jpeg');
+        } finally {
+            unlink($path);
+        }
+    }
+
+    public function testItRejectsTextContent(): void
+    {
+        $path = self::TMP_DIR . '/bf-text-' . bin2hex(random_bytes(4)) . '.txt';
+        self::assertNotFalse(file_put_contents($path, 'this is not an image'));
+
+        try {
+            $this->expectException(InvalidImageException::class);
+            ImageValidator::validate($path, 'image/png');
+        } finally {
+            unlink($path);
+        }
+    }
+
+    public function testItRejectsOversizedFiles(): void
+    {
+        $path = self::TMP_DIR . '/bf-huge-' . bin2hex(random_bytes(4)) . '.png';
+        // Create a 2 MB + 1 byte file
+        $bytes = str_repeat('A', 2_000_001);
+        self::assertNotFalse(file_put_contents($path, $bytes));
+
+        try {
+            $this->expectException(InvalidImageException::class);
+            $this->expectExceptionMessage('exceeds the 2000000 byte limit');
+            ImageValidator::validate($path, 'image/png');
+        } finally {
+            unlink($path);
+        }
+    }
+
+    public function testItRejectsOversizedDimensions(): void
+    {
+        $path = self::TMP_DIR . '/bf-wide-' . bin2hex(random_bytes(4)) . '.png';
+        self::assertNotFalse(file_put_contents($path, self::validPng(600, 8)));
+
+        try {
+            $this->expectException(InvalidImageException::class);
+            $this->expectExceptionMessage('exceed the 512 pixel limit');
+            ImageValidator::validate($path, 'image/png');
+        } finally {
+            unlink($path);
+        }
+    }
+
+    public function testItAcceptsJpegWebpAndGif(): void
+    {
+        $jpeg = self::TMP_DIR . '/bf-jpeg-' . bin2hex(random_bytes(4)) . '.jpg';
+        $webp = self::TMP_DIR . '/bf-webp-' . bin2hex(random_bytes(4)) . '.webp';
+        $gif = self::TMP_DIR . '/bf-gif-' . bin2hex(random_bytes(4)) . '.gif';
+        file_put_contents($jpeg, self::validJpeg(8, 8));
+        file_put_contents($webp, self::validWebp(8, 8));
+        file_put_contents($gif, self::validGif(8, 8));
+
+        try {
+            self::assertSame('jpg', ImageValidator::validate($jpeg, 'image/jpeg')->extension);
+            self::assertSame('webp', ImageValidator::validate($webp, 'image/webp')->extension);
+            self::assertSame('gif', ImageValidator::validate($gif, 'image/gif')->extension);
+        } finally {
+            unlink($jpeg);
+            unlink($webp);
+            unlink($gif);
+        }
+    }
+
+    /**
+     * Build a minimal valid PNG of the given dimensions, using a pre-baked
+     * 8x8 transparent PNG as the base and trusting `getimagesize` to accept
+     * any correctly-formed PNG. We just need the file to (1) have the PNG
+     * magic and (2) be decodable by GD or `getimagesize`.
+     *
+     * For the oversized-dimensions test we synthesize a 600x8 PNG via
+     * `imagecreatetruecolor` + `imagepng` to force the IHDR to claim those
+     * dimensions.
+     */
+    private static function validPng(int $width, int $height): string
+    {
+        if ($width === 8 && $height === 8) {
+            return base64_decode(
+                'iVBORw0KGgoAAAANSUhEUgAAAAgAAAAICAYAAADED76LAAAAFElEQVR4nGNgYGD4z0AswK' .
+                'EWBgYGRgYGBkYGRgAAB4nCH2AAAAAElFTkSuQmCC',
+                true,
+            );
+        }
+
+        $im = imagecreatetruecolor($width, $height);
+        if ($im === false) {
+            throw new \RuntimeException('Failed to create image.');
+        }
+        ob_start();
+        imagepng($im);
+        $bytes = ob_get_clean();
+        imagedestroy($im);
+
+        return (string) $bytes;
+    }
+
+    private static function validJpeg(int $width, int $height): string
+    {
+        $im = imagecreatetruecolor($width, $height);
+        if ($im === false) {
+            throw new \RuntimeException('Failed to create image.');
+        }
+        ob_start();
+        imagejpeg($im);
+        $bytes = ob_get_clean();
+        imagedestroy($im);
+
+        return (string) $bytes;
+    }
+
+    private static function validWebp(int $width, int $height): string
+    {
+        $im = imagecreatetruecolor($width, $height);
+        if ($im === false) {
+            throw new \RuntimeException('Failed to create image.');
+        }
+        ob_start();
+        imagewebp($im);
+        $bytes = ob_get_clean();
+        imagedestroy($im);
+
+        return (string) $bytes;
+    }
+
+    private static function validGif(int $width, int $height): string
+    {
+        $im = imagecreatetruecolor($width, $height);
+        if ($im === false) {
+            throw new \RuntimeException('Failed to create image.');
+        }
+        ob_start();
+        imagegif($im);
+        $bytes = ob_get_clean();
+        imagedestroy($im);
+
+        return (string) $bytes;
+    }
+}