diff --git a/app/Services/ImageGenerationService.php b/app/Services/ImageGenerationService.php
index a7bd3c6..d0ecddc 100644
--- a/app/Services/ImageGenerationService.php
+++ b/app/Services/ImageGenerationService.php
@@ -353,20 +353,27 @@ class ImageGenerationService
     public static function resetIfNotCacheable(?Plugin $plugin): void
     {
         if ($plugin?->id) {
-            // Check if any devices have custom dimensions or use DeviceModels
+            // Check if any devices have custom dimensions or use non-standard DeviceModels
             $hasCustomDimensions = Device::query()
                 ->where(function ($query) {
                     $query->where('width', '!=', 800)
                         ->orWhere('height', '!=', 480)
                         ->orWhere('rotate', '!=', 0);
                 })
-                ->orWhereNotNull('device_model_id')
+                ->orWhereHas('deviceModel', function ($query) {
+                    // Only allow caching if all device models have standard dimensions (800x480, rotation=0)
+                    $query->where(function ($subQuery) {
+                        $subQuery->where('width', '!=', 800)
+                            ->orWhere('height', '!=', 480)
+                            ->orWhere('rotation', '!=', 0);
+                    });
+                })
                 ->exists();
 
             if ($hasCustomDimensions) {
                 // TODO cache image per device
                 $plugin->update(['current_image' => null]);
-                Log::debug('Skip cache as devices with custom dimensions or DeviceModels exist');
+                Log::debug('Skip cache as devices with custom dimensions or non-standard DeviceModels exist');
             }
         }
     }
diff --git a/routes/api.php b/routes/api.php
index c59b539..5f2a9f3 100644
--- a/routes/api.php
+++ b/routes/api.php
@@ -126,10 +126,25 @@ Route::get('/display', function (Request $request) {
             $image_path = 'images/setup-logo.bmp';
             $filename = 'setup-logo.bmp';
         } else {
-            if (isset($device->last_firmware_version)
-                && version_compare($device->last_firmware_version, '1.5.2', '<')
-                && Storage::disk('public')->exists('images/generated/'.$image_uuid.'.bmp')) {
-                $image_path = 'images/generated/'.$image_uuid.'.bmp';
+            // Determine image format based on device settings
+            $preferred_format = 'png'; // Default to PNG for newer firmware
+
+            if (! $device->device_model_id) {
+                // No device model, use device's image_format setting
+                if (str_contains($device->image_format, 'bmp')) {
+                    $preferred_format = 'bmp';
+                }
+                // For 'auto' or unknown formats, fall back to firmware version logic
+                if (isset($device->last_firmware_version)
+                    && version_compare($device->last_firmware_version, '1.5.2', '<')
+                    && Storage::disk('public')->exists('images/generated/'.$image_uuid.'.bmp')) {
+                    $preferred_format = 'bmp';
+                }
+            }
+
+            // Check if a preferred format exists, otherwise fall back
+            if (Storage::disk('public')->exists('images/generated/'.$image_uuid.'.'.$preferred_format)) {
+                $image_path = 'images/generated/'.$image_uuid.'.'.$preferred_format;
             } elseif (Storage::disk('public')->exists('images/generated/'.$image_uuid.'.png')) {
                 $image_path = 'images/generated/'.$image_uuid.'.png';
             } else {
@@ -422,10 +437,25 @@ Route::get('/current_screen', function (Request $request) {
         $image_path = 'images/setup-logo.bmp';
         $filename = 'setup-logo.bmp';
     } else {
-        if (isset($device->last_firmware_version)
-            && version_compare($device->last_firmware_version, '1.5.2', '<')
-            && Storage::disk('public')->exists('images/generated/'.$image_uuid.'.bmp')) {
-            $image_path = 'images/generated/'.$image_uuid.'.bmp';
+        // Determine image format based on device settings
+        $preferred_format = 'png'; // Default to PNG for newer firmware
+
+        if (! $device->device_model_id) {
+            // No device model, use device's image_format setting
+            if (str_contains($device->image_format, 'bmp')) {
+                $preferred_format = 'bmp';
+            }
+            // For 'auto' or unknown formats, fall back to firmware version logic
+            if (isset($device->last_firmware_version)
+                && version_compare($device->last_firmware_version, '1.5.2', '<')
+                && Storage::disk('public')->exists('images/generated/'.$image_uuid.'.bmp')) {
+                $preferred_format = 'bmp';
+            }
+        }
+
+        // Check if preferred format exists, otherwise fall back
+        if (Storage::disk('public')->exists('images/generated/'.$image_uuid.'.'.$preferred_format)) {
+            $image_path = 'images/generated/'.$image_uuid.'.'.$preferred_format;
         } elseif (Storage::disk('public')->exists('images/generated/'.$image_uuid.'.png')) {
             $image_path = 'images/generated/'.$image_uuid.'.png';
         } else {
diff --git a/tests/Feature/Api/DeviceImageFormatTest.php b/tests/Feature/Api/DeviceImageFormatTest.php
index ff24744..fcb7555 100644
--- a/tests/Feature/Api/DeviceImageFormatTest.php
+++ b/tests/Feature/Api/DeviceImageFormatTest.php
@@ -1,6 +1,11 @@
 <?php
 
+use App\Enums\ImageFormat;
 use App\Models\Device;
+use App\Models\Playlist;
+use App\Models\PlaylistItem;
+use App\Models\Plugin;
+use App\Models\User;
 use Illuminate\Support\Facades\Storage;
 
 uses(Illuminate\Foundation\Testing\RefreshDatabase::class);
@@ -118,3 +123,72 @@ test('device falls back to bmp when png does not exist', function () {
             'filename' => 'test-image.bmp',
         ]);
 });
+
+test('device without device_model_id and image_format bmp3_1bit_srgb returns bmp when plugin is rendered', function () {
+    // Create a user with auto-assign enabled
+    $user = User::factory()->create([
+        'assign_new_devices' => true,
+    ]);
+
+    // Create a device without device_model_id and with bmp3_1bit_srgb format
+    $device = Device::factory()->create([
+        'user_id' => $user->id,
+        'mac_address' => '00:11:22:33:44:55',
+        'api_key' => 'test-api-key',
+        'device_model_id' => null, // Explicitly set to null
+        'image_format' => ImageFormat::BMP3_1BIT_SRGB->value,
+        'last_firmware_version' => '1.5.2',
+    ]);
+
+    // Create a plugin
+    $plugin = Plugin::factory()->create([
+        'user_id' => $user->id,
+        'name' => 'Test Plugin',
+        'render_markup' => '<div>Test Content</div>',
+        'data_strategy' => 'static',
+        'markup_language' => 'blade',
+        'current_image' => 'test-generated-image', // Set current image directly
+    ]);
+
+    // Create a playlist for the device
+    $playlist = Playlist::factory()->create([
+        'device_id' => $device->id,
+        'is_active' => true,
+        'refresh_time' => 900,
+    ]);
+
+    // Create a playlist item with the plugin
+    $playlistItem = PlaylistItem::factory()->create([
+        'playlist_id' => $playlist->id,
+        'plugin_id' => $plugin->id,
+        'is_active' => true,
+        'order' => 1,
+    ]);
+
+    // Mock the image generation to create both bmp and png files
+    $imageUuid = 'test-generated-image';
+    Storage::disk('public')->put('images/generated/'.$imageUuid.'.bmp', 'fake bmp content');
+    Storage::disk('public')->put('images/generated/'.$imageUuid.'.png', 'fake png content');
+
+    // Set the device's current screen image to the plugin's image
+    $device->update(['current_screen_image' => $imageUuid]);
+
+    // Test /api/display endpoint
+    $displayResponse = $this->withHeaders([
+        'id' => $device->mac_address,
+        'access-token' => $device->api_key,
+        'rssi' => -70,
+        'battery_voltage' => 3.8,
+        'fw-version' => '1.5.2',
+    ])->get('/api/current_screen');
+
+    $displayResponse->assertOk();
+    $displayResponse->assertJson([
+        'filename' => $imageUuid.'.bmp',
+    ]);
+
+    // Verify that the device's image_format is correctly set
+    $device->refresh();
+    expect($device->image_format)->toBe(ImageFormat::BMP3_1BIT_SRGB->value)
+        ->and($device->device_model_id)->toBeNull();
+});
diff --git a/tests/Feature/ImageGenerationServiceTest.php b/tests/Feature/ImageGenerationServiceTest.php
index 22699c5..fc06a5b 100644
--- a/tests/Feature/ImageGenerationServiceTest.php
+++ b/tests/Feature/ImageGenerationServiceTest.php
@@ -423,3 +423,35 @@ it('determines correct image format from device model', function (): void {
     expect($device3->current_screen_image)->toBe($uuid3);
     Storage::disk('public')->assertExists("/images/generated/{$uuid3}.png");
 })->skipOnGitHubActions();
+
+it('generates BMP for legacy device with bmp3_1bit_srgb format', function (): void {
+    // Create a device with BMP format but no DeviceModel (legacy behavior)
+    $device = Device::factory()->create([
+        'width' => 800,
+        'height' => 480,
+        'rotate' => 0,
+        'image_format' => ImageFormat::BMP3_1BIT_SRGB->value,
+        'device_model_id' => null, // Explicitly no DeviceModel
+    ]);
+
+    $markup = '<div style="background: white; color: black; padding: 20px;">Test Content</div>';
+    $uuid = ImageGenerationService::generateImage($markup, $device->id);
+
+    // Assert the device was updated with a new image UUID
+    $device->refresh();
+    expect($device->current_screen_image)->toBe($uuid);
+
+    // Assert BMP file was created
+    Storage::disk('public')->assertExists("/images/generated/{$uuid}.bmp");
+
+    // Verify the BMP file has content and isn't blank
+    $imagePath = Storage::disk('public')->path("/images/generated/{$uuid}.bmp");
+    $imageSize = filesize($imagePath);
+    expect($imageSize)->toBeGreaterThan(100); // Should be at least 100 bytes for a BMP
+
+    // Verify it's a valid BMP file
+    $imageInfo = getimagesize($imagePath);
+    expect($imageInfo[0])->toBe(800); // Width
+    expect($imageInfo[1])->toBe(480); // Height
+    expect($imageInfo[2])->toBe(IMAGETYPE_BMP); // BMP type
+})->skipOnGitHubActions();
diff --git a/tests/Unit/Services/ImageGenerationServiceTest.php b/tests/Unit/Services/ImageGenerationServiceTest.php
index 4941c3c..b254243 100644
--- a/tests/Unit/Services/ImageGenerationServiceTest.php
+++ b/tests/Unit/Services/ImageGenerationServiceTest.php
@@ -226,6 +226,59 @@ it('reset_if_not_cacheable preserves cache for standard devices', function (): v
     expect($plugin->current_image)->toBe('test-uuid');
 })->skipOnGitHubActions();
 
+it('reset_if_not_cacheable preserves cache for og_png and og_plus device models', function (): void {
+    // Create a plugin
+    $plugin = App\Models\Plugin::factory()->create(['current_image' => 'test-uuid']);
+
+    // Create og_png device model
+    $ogPngModel = DeviceModel::factory()->create([
+        'name' => 'test_og_png',
+        'width' => 800,
+        'height' => 480,
+        'rotation' => 0,
+    ]);
+
+    // Create og_plus device model
+    $ogPlusModel = DeviceModel::factory()->create([
+        'name' => 'test_og_plus',
+        'width' => 800,
+        'height' => 480,
+        'rotation' => 0,
+    ]);
+
+    // Create devices with og_png and og_plus device models
+    Device::factory()->create(['device_model_id' => $ogPngModel->id]);
+    Device::factory()->create(['device_model_id' => $ogPlusModel->id]);
+
+    // Test that the method preserves cache for standard device models
+    ImageGenerationService::resetIfNotCacheable($plugin);
+
+    $plugin->refresh();
+    expect($plugin->current_image)->toBe('test-uuid');
+})->skipOnGitHubActions();
+
+it('reset_if_not_cacheable resets cache for non-standard device models', function (): void {
+    // Create a plugin
+    $plugin = App\Models\Plugin::factory()->create(['current_image' => 'test-uuid']);
+
+    // Create a non-standard device model (e.g., kindle)
+    $kindleModel = DeviceModel::factory()->create([
+        'name' => 'test_amazon_kindle_2024',
+        'width' => 1400,
+        'height' => 840,
+        'rotation' => 90,
+    ]);
+
+    // Create a device with the non-standard device model
+    Device::factory()->create(['device_model_id' => $kindleModel->id]);
+
+    // Test that the method resets cache for non-standard device models
+    ImageGenerationService::resetIfNotCacheable($plugin);
+
+    $plugin->refresh();
+    expect($plugin->current_image)->toBeNull();
+})->skipOnGitHubActions();
+
 it('reset_if_not_cacheable handles null plugin', function (): void {
     // Test that the method handles null plugin gracefully
     expect(fn () => ImageGenerationService::resetIfNotCacheable(null))->not->toThrow(Exception::class);