diff --git a/app/Modules/Lemmy/Services/LemmyPublisher.php b/app/Modules/Lemmy/Services/LemmyPublisher.php
index 11d7e300..cce698d3 100644
--- a/app/Modules/Lemmy/Services/LemmyPublisher.php
+++ b/app/Modules/Lemmy/Services/LemmyPublisher.php
@@ -7,6 +7,7 @@
 use App\Models\PlatformAccount;
 use App\Models\PlatformChannel;
 use App\Services\Auth\LemmyAuthService;
+use App\Services\Log\LogSaver;
 use Exception;
 
 class LemmyPublisher
@@ -15,10 +16,13 @@ class LemmyPublisher
 
     private PlatformAccount $account;
 
+    private ThumbnailUploader $thumbnailUploader;
+
     public function __construct(PlatformAccount $account)
     {
         $this->api = new LemmyApiService($account->instance_url);
         $this->account = $account;
+        $this->thumbnailUploader = new ThumbnailUploader($account->instance_url);
     }
 
     /**
@@ -54,13 +58,25 @@ private function createPost(string $token, array $extractedData, PlatformChannel
     {
         $languageId = $extractedData['language_id'] ?? null;
 
+        $thumbnail = $extractedData['thumbnail'] ?? null;
+        $thumbnail = is_string($thumbnail) && $thumbnail !== '' ? $thumbnail : null;
+
+        $hosted = $this->thumbnailUploader->upload($thumbnail, $token);
+
+        if ($thumbnail !== null && $hosted === null) {
+            resolve(LogSaver::class)->warning('Thumbnail upload failed; publishing without one', $channel, [
+                'article_id' => $article->id,
+                'source' => $thumbnail,
+            ]);
+        }
+
         return $this->api->createPost(
             $token,
             $extractedData['title'] ?? 'Untitled',
             $extractedData['description'] ?? '',
             $channel->channel_id,
             $article->url,
-            $extractedData['thumbnail'] ?? null,
+            $hosted,
             $languageId
         );
     }
diff --git a/app/Modules/Lemmy/Services/ThumbnailUploader.php b/app/Modules/Lemmy/Services/ThumbnailUploader.php
new file mode 100644
index 00000000..c6209eb9
--- /dev/null
+++ b/app/Modules/Lemmy/Services/ThumbnailUploader.php
@@ -0,0 +1,125 @@
+<?php
+
+namespace App\Modules\Lemmy\Services;
+
+use App\Modules\Lemmy\LemmyRequest;
+use Illuminate\Support\Facades\Http;
+use Throwable;
+
+class ThumbnailUploader
+{
+    private const MAX_WIDTH = 600;
+
+    // A 4000x2256 JPEG decodes to ~27MB in GD; the worker runs with memory_limit=128M.
+    private const MAX_SOURCE_BYTES = 10_485_760;
+
+    private const MAX_SOURCE_PIXELS = 50_000_000;
+
+    private const JPEG_QUALITY = 82;
+
+    public function __construct(private string $instance) {}
+
+    /**
+     * Returns an instance-hosted URL for a downscaled copy, or null if anything fails.
+     */
+    public function upload(?string $sourceUrl, string $token): ?string
+    {
+        if ($sourceUrl === null || $sourceUrl === '') {
+            return null;
+        }
+
+        try {
+            $source = $this->download($sourceUrl);
+
+            if ($source === null) {
+                return null;
+            }
+
+            $resized = $this->resize($source);
+
+            if ($resized === null) {
+                return null;
+            }
+
+            return $this->store($resized, $token);
+        } catch (Throwable) {
+            return null;
+        }
+    }
+
+    private function download(string $url): ?string
+    {
+        $response = Http::timeout(30)->get($url);
+
+        if (! $response->successful()) {
+            return null;
+        }
+
+        $body = $response->body();
+
+        return strlen($body) > self::MAX_SOURCE_BYTES ? null : $body;
+    }
+
+    private function resize(string $source): ?string
+    {
+        $info = @getimagesizefromstring($source);
+
+        if ($info === false) {
+            return null;
+        }
+
+        [$width, $height] = $info;
+
+        if ($width < 1 || $height < 1 || $width * $height > self::MAX_SOURCE_PIXELS) {
+            return null;
+        }
+
+        if ($width <= self::MAX_WIDTH) {
+            return $source;
+        }
+
+        $image = @imagecreatefromstring($source);
+
+        if ($image === false) {
+            return null;
+        }
+
+        $targetHeight = (int) max(1, round($height * (self::MAX_WIDTH / $width)));
+        $resized = imagescale($image, self::MAX_WIDTH, $targetHeight);
+        imagedestroy($image);
+
+        if ($resized === false) {
+            return null;
+        }
+
+        ob_start();
+
+        try {
+            imagejpeg($resized, null, self::JPEG_QUALITY);
+        } finally {
+            $bytes = (string) ob_get_clean();
+            imagedestroy($resized);
+        }
+
+        return $bytes === '' ? null : $bytes;
+    }
+
+    private function store(string $bytes, string $token): ?string
+    {
+        $response = (new LemmyRequest($this->instance, $token))
+            ->postMultipart('pictrs/image', 'images[]', $bytes, 'thumbnail.jpg');
+
+        if (! $response->successful()) {
+            return null;
+        }
+
+        $file = $response->json('files.0.file');
+
+        if (! is_string($file) || $file === '') {
+            return null;
+        }
+
+        // $instance is a full scheme-qualified URL — platform_accounts.instance_url is validated as a URL.
+        return sprintf('%s/pictrs/image/%s', rtrim($this->instance, '/'), $file);
+    }
+}
diff --git a/tests/Unit/Modules/Lemmy/Services/LemmyPublisherTest.php b/tests/Unit/Modules/Lemmy/Services/LemmyPublisherTest.php
index 1781ffc0..3e53f211 100644
--- a/tests/Unit/Modules/Lemmy/Services/LemmyPublisherTest.php
+++ b/tests/Unit/Modules/Lemmy/Services/LemmyPublisherTest.php
@@ -9,7 +9,9 @@
 use App\Models\PlatformChannel;
 use App\Modules\Lemmy\Services\LemmyApiService;
 use App\Modules\Lemmy\Services\LemmyPublisher;
+use App\Modules\Lemmy\Services\ThumbnailUploader;
 use App\Services\Auth\LemmyAuthService;
+use App\Services\Log\LogSaver;
 use Exception;
 use Illuminate\Foundation\Testing\RefreshDatabase;
 use Mockery;
@@ -25,6 +27,29 @@ protected function tearDown(): void
         parent::tearDown();
     }
 
+    /**
+     * Swaps in a mocked API and an uploader that echoes its input back, so existing
+     * expectations can keep asserting on the thumbnail they passed in.
+     */
+    private function injectMocks(LemmyPublisher $publisher, LemmyApiService $api, ?ThumbnailUploader $uploader = null): void
+    {
+        if (! $uploader instanceof ThumbnailUploader) {
+            $passthrough = Mockery::mock(ThumbnailUploader::class);
+            $passthrough->shouldReceive('upload')->andReturnUsing(fn (?string $url): ?string => $url);
+            $uploader = $passthrough;
+        }
+
+        $reflection = new \ReflectionClass($publisher);
+
+        $apiProperty = $reflection->getProperty('api');
+        $apiProperty->setAccessible(true);
+        $apiProperty->setValue($publisher, $api);
+
+        $uploaderProperty = $reflection->getProperty('thumbnailUploader');
+        $uploaderProperty->setAccessible(true);
+        $uploaderProperty->setValue($publisher, $uploader);
+    }
+
     public function test_constructor_initializes_api_service(): void
     {
         $account = PlatformAccount::factory()->make([
@@ -92,10 +117,7 @@ public function test_publish_to_channel_with_all_data(): void
         // Create publisher and inject mocked API using reflection
         $publisher = new LemmyPublisher($account);
 
-        $reflection = new \ReflectionClass($publisher);
-        $apiProperty = $reflection->getProperty('api');
-        $apiProperty->setAccessible(true);
-        $apiProperty->setValue($publisher, $apiMock);
+        $this->injectMocks($publisher, $apiMock);
 
         $result = $publisher->publishToChannel($article, $extractedData, $channel);
 
@@ -145,10 +167,7 @@ public function test_publish_to_channel_with_minimal_data(): void
         // Create publisher and inject mocked API using reflection
         $publisher = new LemmyPublisher($account);
 
-        $reflection = new \ReflectionClass($publisher);
-        $apiProperty = $reflection->getProperty('api');
-        $apiProperty->setAccessible(true);
-        $apiProperty->setValue($publisher, $apiMock);
+        $this->injectMocks($publisher, $apiMock);
 
         $result = $publisher->publishToChannel($article, $extractedData, $channel);
 
@@ -201,10 +220,7 @@ public function test_publish_to_channel_without_thumbnail(): void
         // Create publisher and inject mocked API using reflection
         $publisher = new LemmyPublisher($account);
 
-        $reflection = new \ReflectionClass($publisher);
-        $apiProperty = $reflection->getProperty('api');
-        $apiProperty->setAccessible(true);
-        $apiProperty->setValue($publisher, $apiMock);
+        $this->injectMocks($publisher, $apiMock);
 
         $result = $publisher->publishToChannel($article, $extractedData, $channel);
 
@@ -273,10 +289,7 @@ public function test_publish_to_channel_throws_api_exception(): void
         // Create publisher and inject mocked API using reflection
         $publisher = new LemmyPublisher($account);
 
-        $reflection = new \ReflectionClass($publisher);
-        $apiProperty = $reflection->getProperty('api');
-        $apiProperty->setAccessible(true);
-        $apiProperty->setValue($publisher, $apiMock);
+        $this->injectMocks($publisher, $apiMock);
 
         $this->expectException(Exception::class);
         $this->expectExceptionMessage('API Error');
@@ -327,13 +340,99 @@ public function test_publish_to_channel_forwards_resolved_community_id_to_create
         // Create publisher and inject mocked API using reflection
         $publisher = new LemmyPublisher($account);
 
-        $reflection = new \ReflectionClass($publisher);
-        $apiProperty = $reflection->getProperty('api');
-        $apiProperty->setAccessible(true);
-        $apiProperty->setValue($publisher, $apiMock);
+        $this->injectMocks($publisher, $apiMock);
 
         $result = $publisher->publishToChannel($article, $extractedData, $channel);
 
         $this->assertEquals(['success' => true], $result);
     }
+
+    public function test_it_passes_the_uploaded_thumbnail_url_to_create_post(): void
+    {
+        $account = PlatformAccount::factory()->make(['instance_url' => 'https://lemmy.world']);
+        $article = Article::factory()->make(['url' => 'https://example.com/article']);
+        $channel = PlatformChannel::factory()->make(['channel_id' => 7]);
+
+        $authMock = Mockery::mock(LemmyAuthService::class);
+        $authMock->shouldReceive('getToken')->andReturn('tok');
+        $this->app->instance(LemmyAuthService::class, $authMock);
+
+        $apiMock = Mockery::mock(LemmyApiService::class);
+        $apiMock->shouldReceive('createPost')
+            ->once()
+            ->with('tok', 'T', '', 7, 'https://example.com/article', 'https://lemmy.world/pictrs/image/x.jpg', null)
+            ->andReturn(['ok' => true]);
+
+        $uploader = Mockery::mock(ThumbnailUploader::class);
+        $uploader->shouldReceive('upload')
+            ->once()
+            ->with('https://cdn.example.com/big.jpg', 'tok')
+            ->andReturn('https://lemmy.world/pictrs/image/x.jpg');
+
+        $publisher = new LemmyPublisher($account);
+        $this->injectMocks($publisher, $apiMock, $uploader);
+
+        $this->assertSame(
+            ['ok' => true],
+            $publisher->publishToChannel($article, ['title' => 'T', 'thumbnail' => 'https://cdn.example.com/big.jpg'], $channel)
+        );
+    }
+
+    public function test_it_logs_a_warning_when_the_thumbnail_upload_fails(): void
+    {
+        $account = PlatformAccount::factory()->make(['instance_url' => 'https://lemmy.world']);
+        $article = Article::factory()->create();
+        $channel = PlatformChannel::factory()->create();
+
+        $authMock = Mockery::mock(LemmyAuthService::class);
+        $authMock->shouldReceive('getToken')->andReturn('tok');
+        $this->app->instance(LemmyAuthService::class, $authMock);
+
+        $logMock = Mockery::mock(LogSaver::class);
+        $logMock->shouldReceive('warning')
+            ->once()
+            ->withArgs(fn (string $message, ?PlatformChannel $c, array $context): bool => str_contains($message, 'Thumbnail upload failed')
+                && $context['source'] === 'https://cdn.example.com/big.jpg');
+        $this->app->instance(LogSaver::class, $logMock);
+
+        $apiMock = Mockery::mock(LemmyApiService::class);
+        $apiMock->shouldReceive('createPost')->once()->andReturn(['ok' => true]);
+
+        $uploader = Mockery::mock(ThumbnailUploader::class);
+        $uploader->shouldReceive('upload')->once()->andReturn(null);
+
+        $publisher = new LemmyPublisher($account);
+        $this->injectMocks($publisher, $apiMock, $uploader);
+
+        $this->assertSame(
+            ['ok' => true],
+            $publisher->publishToChannel($article, ['title' => 'T', 'thumbnail' => 'https://cdn.example.com/big.jpg'], $channel)
+        );
+    }
+
+    public function test_it_does_not_log_when_there_was_no_thumbnail_to_upload(): void
+    {
+        $account = PlatformAccount::factory()->make(['instance_url' => 'https://lemmy.world']);
+        $article = Article::factory()->make(['url' => 'https://example.com/article']);
+        $channel = PlatformChannel::factory()->make(['channel_id' => 7]);
+
+        $authMock = Mockery::mock(LemmyAuthService::class);
+        $authMock->shouldReceive('getToken')->andReturn('tok');
+        $this->app->instance(LemmyAuthService::class, $authMock);
+
+        $logMock = Mockery::mock(LogSaver::class);
+        $logMock->shouldNotReceive('warning');
+        $this->app->instance(LogSaver::class, $logMock);
+
+        $apiMock = Mockery::mock(LemmyApiService::class);
+        $apiMock->shouldReceive('createPost')->once()->andReturn(['ok' => true]);
+
+        $uploader = Mockery::mock(ThumbnailUploader::class);
+        $uploader->shouldReceive('upload')->once()->with(null, 'tok')->andReturn(null);
+
+        $publisher = new LemmyPublisher($account);
+        $this->injectMocks($publisher, $apiMock, $uploader);
+
+        $this->assertSame(['ok' => true], $publisher->publishToChannel($article, ['title' => 'T'], $channel));
+    }
 }
diff --git a/tests/Unit/Modules/Lemmy/Services/ThumbnailUploaderTest.php b/tests/Unit/Modules/Lemmy/Services/ThumbnailUploaderTest.php
new file mode 100644
index 00000000..10a332a5
--- /dev/null
+++ b/tests/Unit/Modules/Lemmy/Services/ThumbnailUploaderTest.php
@@ -0,0 +1,168 @@
+<?php
+
+namespace Tests\Unit\Modules\Lemmy\Services;
+
+use App\Modules\Lemmy\Services\ThumbnailUploader;
+use Illuminate\Http\Client\Request;
+use Illuminate\Support\Facades\Http;
+use Tests\TestCase;
+
+class ThumbnailUploaderTest extends TestCase
+{
+    /**
+     * @param  int<1, max>  $width
+     * @param  int<1, max>  $height
+     */
+    private function jpeg(int $width, int $height): string
+    {
+        $image = imagecreatetruecolor($width, $height);
+        $colour = imagecolorallocate($image, 120, 90, 60);
+        imagefilledrectangle($image, 0, 0, $width - 1, $height - 1, $colour === false ? 0 : $colour);
+
+        ob_start();
+        imagejpeg($image, null, 90);
+        $bytes = (string) ob_get_clean();
+        imagedestroy($image);
+
+        return $bytes;
+    }
+
+    private function uploader(): ThumbnailUploader
+    {
+        return new ThumbnailUploader('https://lemmy.world');
+    }
+
+    private function fake(string $sourceBody, mixed $uploadResponse, int $uploadStatus = 200): void
+    {
+        Http::fake([
+            'https://cdn.example.com/*' => Http::response($sourceBody, 200, ['Content-Type' => 'image/jpeg']),
+            'https://lemmy.world/pictrs/image' => Http::response($uploadResponse, $uploadStatus),
+        ]);
+    }
+
+    public function test_it_returns_an_instance_hosted_url(): void
+    {
+        $this->fake($this->jpeg(1200, 800), ['files' => [['file' => 'abc123.jpg', 'delete_token' => 'tok']]]);
+
+        $url = $this->uploader()->upload('https://cdn.example.com/big.jpg', 'token');
+
+        $this->assertSame('https://lemmy.world/pictrs/image/abc123.jpg', $url);
+    }
+
+    public function test_it_downscales_a_wide_image_before_upload(): void
+    {
+        $source = $this->jpeg(2000, 1000);
+        $this->fake($source, ['files' => [['file' => 'abc123.jpg']]]);
+
+        $this->uploader()->upload('https://cdn.example.com/big.jpg', 'token');
+
+        Http::assertSent(function (Request $request) use ($source): bool {
+            if ($request->url() !== 'https://lemmy.world/pictrs/image') {
+                return false;
+            }
+
+            $uploaded = $this->multipartFileContents($request);
+            $size = getimagesizefromstring($uploaded);
+
+            return $size !== false
+                && $size[0] === 600
+                && $size[1] === 300
+                && $uploaded !== $source
+                && strlen($uploaded) < strlen($source);
+        });
+    }
+
+    public function test_it_uploads_a_small_image_untouched(): void
+    {
+        $source = $this->jpeg(320, 240);
+        $this->fake($source, ['files' => [['file' => 'abc123.jpg']]]);
+
+        $this->uploader()->upload('https://cdn.example.com/small.jpg', 'token');
+
+        Http::assertSent(function (Request $request) use ($source): bool {
+            return $request->url() !== 'https://lemmy.world/pictrs/image'
+                || $this->multipartFileContents($request) === $source;
+        });
+    }
+
+    public function test_it_sends_the_token_as_a_bearer_header(): void
+    {
+        $this->fake($this->jpeg(800, 600), ['files' => [['file' => 'abc123.jpg']]]);
+
+        $this->uploader()->upload('https://cdn.example.com/big.jpg', 'secret-token');
+
+        Http::assertSent(fn (Request $request): bool => $request->url() !== 'https://lemmy.world/pictrs/image'
+            || $request->header('Authorization')[0] === 'Bearer secret-token');
+    }
+
+    public function test_it_returns_null_for_a_null_source(): void
+    {
+        Http::fake();
+
+        $this->assertNull($this->uploader()->upload(null, 'token'));
+
+        Http::assertNothingSent();
+    }
+
+    public function test_it_returns_null_for_an_empty_source(): void
+    {
+        Http::fake();
+
+        $this->assertNull($this->uploader()->upload('', 'token'));
+
+        Http::assertNothingSent();
+    }
+
+    public function test_it_returns_null_when_the_download_fails(): void
+    {
+        Http::fake(['https://cdn.example.com/*' => Http::response('', 404)]);
+
+        $this->assertNull($this->uploader()->upload('https://cdn.example.com/gone.jpg', 'token'));
+    }
+
+    public function test_it_returns_null_when_the_source_is_not_an_image(): void
+    {
+        $this->fake('<html>not an image</html>', ['files' => [['file' => 'abc123.jpg']]]);
+
+        $this->assertNull($this->uploader()->upload('https://cdn.example.com/page.html', 'token'));
+    }
+
+    public function test_it_returns_null_when_the_upload_fails(): void
+    {
+        $this->fake($this->jpeg(1200, 800), ['error' => 'nope'], 500);
+
+        $this->assertNull($this->uploader()->upload('https://cdn.example.com/big.jpg', 'token'));
+    }
+
+    public function test_it_returns_null_when_the_upload_response_has_no_file(): void
+    {
+        $this->fake($this->jpeg(1200, 800), ['files' => []]);
+
+        $this->assertNull($this->uploader()->upload('https://cdn.example.com/big.jpg', 'token'));
+    }
+
+    public function test_it_returns_null_when_the_source_exceeds_the_size_cap(): void
+    {
+        $this->fake(str_repeat('x', 10_485_761), ['files' => [['file' => 'abc123.jpg']]]);
+
+        $this->assertNull($this->uploader()->upload('https://cdn.example.com/huge.jpg', 'token'));
+    }
+
+    public function test_it_returns_null_when_the_download_throws(): void
+    {
+        Http::fake(fn () => throw new \RuntimeException('connection refused'));
+
+        $this->assertNull($this->uploader()->upload('https://cdn.example.com/big.jpg', 'token'));
+    }
+
+    private function multipartFileContents(Request $request): string
+    {
+        foreach ($request->data() as $part) {
+            if (($part['name'] ?? null) === 'images[]') {
+                return (string) $part['contents'];
+            }
+        }
+
+        return '';
+    }
+}