diff --git a/tests/test_media_upload.py b/tests/test_media_upload.py
index 02bb328..3c2fd01 100644
--- a/tests/test_media_upload.py
+++ b/tests/test_media_upload.py
@@ -74,6 +74,31 @@ def create_test_heic(width=800, height=600):
     return buffer.getvalue()
 
 
+def create_test_mpo(width=800, height=600):
+    """
+    Generate test MPO (Multi-Picture Object) image
+
+    MPO format is used by iPhones for depth/portrait photos. It contains
+    multiple JPEG images in one file. For testing, we create a simple MPO
+    with a single frame.
+
+    Args:
+        width: Image width in pixels
+        height: Image height in pixels
+
+    Returns:
+        Bytes of MPO image data
+    """
+    # Create a simple RGB image
+    img = Image.new('RGB', (width, height), color='green')
+
+    # Save as MPO (Pillow will handle this correctly)
+    buffer = io.BytesIO()
+    img.save(buffer, format='MPO', quality=95)
+    buffer.seek(0)
+    return buffer.getvalue()
+
+
 class TestImageValidation:
     """Test validate_image function"""
 
@@ -236,6 +261,54 @@ class TestHEICSupport:
             assert saved_img.format == 'JPEG'
 
 
+class TestMPOSupport:
+    """Test MPO (Multi-Picture Object) image format support (v1.5.0 Phase 5)"""
+
+    def test_mpo_detection_and_conversion(self):
+        """Test MPO file is detected and converted to JPEG"""
+        mpo_data = create_test_mpo(800, 600)
+        file_data, mime_type, width, height = validate_image(mpo_data, 'test.mpo')
+
+        # Should be converted to JPEG
+        assert mime_type == 'image/jpeg'
+        assert width == 800
+        assert height == 600
+        # Verify it's actually JPEG by opening it
+        img = Image.open(io.BytesIO(file_data))
+        assert img.format == 'JPEG'
+        # Note: MPO with single frame may have identical bytes to JPEG
+        # The important part is the format detection and MIME type correction
+
+    def test_mpo_dimensions_preserved(self):
+        """Test MPO conversion preserves dimensions"""
+        mpo_data = create_test_mpo(1024, 768)
+        file_data, mime_type, width, height = validate_image(mpo_data, 'photo.mpo')
+
+        assert width == 1024
+        assert height == 768
+        assert mime_type == 'image/jpeg'
+
+    def test_mpo_full_upload_flow(self, app):
+        """Test complete MPO upload through save_media"""
+        mpo_data = create_test_mpo(800, 600)
+
+        with app.app_context():
+            media_info = save_media(mpo_data, 'iphone_portrait.mpo')
+
+            # Should be saved as JPEG
+            assert media_info['mime_type'] == 'image/jpeg'
+            assert media_info['width'] == 800
+            assert media_info['height'] == 600
+
+            # Verify file was saved
+            media_path = Path(app.config['DATA_PATH']) / 'media' / media_info['path']
+            assert media_path.exists()
+
+            # Verify it's actually a JPEG file
+            saved_img = Image.open(media_path)
+            assert saved_img.format == 'JPEG'
+
+
 class TestImageOptimization:
     """Test optimize_image function"""