diff --git a/src/Application/ImageUploadService.php b/src/Application/ImageUploadService.php
new file mode 100644
index 0000000..c375eee
--- /dev/null
+++ b/src/Application/ImageUploadService.php
@@ -0,0 +1,38 @@
+<?php
+
+declare(strict_types=1);
+
+namespace BattleForge\Application;
+
+final class ImageUploadService
+{
+    public function __construct(
+        private readonly string $userToken,
+        private readonly string $uploadsRoot,
+    ) {
+    }
+
+    public function store(string $tempPath, string $declaredMime): string
+    {
+        $validated = ImageValidator::validate($tempPath, $declaredMime);
+
+        $namespace = $this->uploadsRoot . '/' . $this->userToken;
+        if (!is_dir($namespace)) {
+            mkdir($namespace, 0700, true);
+        }
+
+        $hash = bin2hex(random_bytes(16));
+        $filename = $hash . '.' . $validated->extension;
+        $destination = $namespace . '/' . $filename;
+
+        if (!rename($tempPath, $destination)) {
+            throw new InvalidImageException("Could not move upload to {$destination}.");
+        }
+
+        // Lock the file down: the namespace is already 0700; tighten the
+        // file itself to 0600 in case the server's umask is permissive.
+        chmod($destination, 0600);
+
+        return '/assets/' . $this->userToken . '/' . $filename;
+    }
+}
diff --git a/tests/Unit/Application/ImageUploadServiceTest.php b/tests/Unit/Application/ImageUploadServiceTest.php
new file mode 100644
index 0000000..a80cfdd
--- /dev/null
+++ b/tests/Unit/Application/ImageUploadServiceTest.php
@@ -0,0 +1,94 @@
+<?php
+
+declare(strict_types=1);
+
+namespace BattleForge\Tests\Unit\Application;
+
+use BattleForge\Application\ImageUploadService;
+use PHPUnit\Framework\TestCase;
+
+final class ImageUploadServiceTest extends TestCase
+{
+    private string $tmpDir;
+
+    protected function setUp(): void
+    {
+        $this->tmpDir = sys_get_temp_dir() . '/bf-uploads-' . bin2hex(random_bytes(4));
+        mkdir($this->tmpDir, 0700, true);
+    }
+
+    protected function tearDown(): void
+    {
+        if (is_dir($this->tmpDir)) {
+            foreach (glob($this->tmpDir . '/*/*') as $file) {
+                unlink($file);
+            }
+            foreach (glob($this->tmpDir . '/*') as $dir) {
+                rmdir($dir);
+            }
+            rmdir($this->tmpDir);
+        }
+    }
+
+    public function testItStoresAValidImageAndReturnsAStableUrl(): void
+    {
+        $service = new ImageUploadService('user-token-1', $this->tmpDir);
+        $tmp = tempnam(sys_get_temp_dir(), 'bf-up');
+        file_put_contents($tmp, self::validPng(8, 8));
+
+        $url = $service->store($tmp, 'image/png');
+
+        self::assertStringStartsWith('/assets/user-token-1/', $url);
+        self::assertStringEndsWith('.png', $url);
+
+        $stored = $this->tmpDir . '/user-token-1/' . basename($url);
+        self::assertFileExists($stored);
+    }
+
+    public function testItCreatesTheUserNamespaceDirectory(): void
+    {
+        $service = new ImageUploadService('fresh-user', $this->tmpDir);
+        $tmp = tempnam(sys_get_temp_dir(), 'bf-up');
+        file_put_contents($tmp, self::validPng(8, 8));
+
+        $service->store($tmp, 'image/png');
+
+        self::assertDirectoryExists($this->tmpDir . '/fresh-user');
+    }
+
+    public function testItProducesUniqueFilenamesForRepeatedUploads(): void
+    {
+        $service = new ImageUploadService('user-token-2', $this->tmpDir);
+        $tmp1 = tempnam(sys_get_temp_dir(), 'bf-up');
+        $tmp2 = tempnam(sys_get_temp_dir(), 'bf-up');
+        file_put_contents($tmp1, self::validPng(8, 8));
+        file_put_contents($tmp2, self::validPng(8, 8));
+
+        $url1 = $service->store($tmp1, 'image/png');
+        $url2 = $service->store($tmp2, 'image/png');
+
+        self::assertNotSame($url1, $url2);
+    }
+
+    public function testItRejectsAnInvalidImage(): void
+    {
+        $service = new ImageUploadService('user-token-3', $this->tmpDir);
+        $tmp = tempnam(sys_get_temp_dir(), 'bf-up');
+        file_put_contents($tmp, 'not an image');
+
+        $this->expectException(\BattleForge\Application\InvalidImageException::class);
+        $service->store($tmp, 'image/png');
+    }
+
+    private static function validPng(int $width, int $height): string
+    {
+        if ($width === 8 && $height === 8) {
+            return base64_decode(
+                'iVBORw0KGgoAAAANSUhEUgAAAAgAAAAICAYAAADED76LAAAAFElEQVR4nGNgYGD4z0AswK' .
+                'EWBgYGRgYGBkYGRgAAB4nCH2AAAAAElFTkSuQmCC',
+                true,
+            );
+        }
+        throw new \InvalidArgumentException('Only 8x8 base PNG supported in tests.');
+    }
+}