diff --git a/decart/models.py b/decart/models.py
index a63cbe9..7a3cbe7 100644
--- a/decart/models.py
+++ b/decart/models.py
@@ -113,6 +113,7 @@ class ImageToImageInput(DecartBaseModel):
         max_length=1000,
     )
     data: FileInput
+    reference_image: Optional[FileInput] = None
     seed: Optional[int] = None
     resolution: Optional[str] = None
     enhance_prompt: Optional[bool] = None
diff --git a/decart/process/request.py b/decart/process/request.py
index 9f6b132..49ff7d2 100644
--- a/decart/process/request.py
+++ b/decart/process/request.py
@@ -89,7 +89,7 @@ async def send_request(
 
     for key, value in inputs.items():
         if value is not None:
-            if key in ("data", "start", "end"):
+            if key in ("data", "start", "end", "reference_image"):
                 content, content_type = await file_input_to_bytes(value, session)
                 form_data.add_field(key, content, content_type=content_type)
             else:
diff --git a/tests/test_process.py b/tests/test_process.py
index 736bd7e..007c5b7 100644
--- a/tests/test_process.py
+++ b/tests/test_process.py
@@ -41,6 +41,38 @@ async def test_process_image_to_image() -> None:
         assert result == b"fake image data"
 
 
+@pytest.mark.asyncio
+async def test_process_image_to_image_with_reference_image() -> None:
+    """Test image-to-image with optional reference_image."""
+    client = DecartClient(api_key="test-key")
+
+    with patch("aiohttp.ClientSession") as mock_session_cls:
+        mock_response = MagicMock()
+        mock_response.ok = True
+        mock_response.read = AsyncMock(return_value=b"fake image data")
+
+        mock_session = MagicMock()
+        mock_session.__aenter__ = AsyncMock(return_value=mock_session)
+        mock_session.__aexit__ = AsyncMock(return_value=None)
+        mock_session.post = MagicMock()
+        mock_session.post.return_value.__aenter__ = AsyncMock(return_value=mock_response)
+        mock_session.post.return_value.__aexit__ = AsyncMock(return_value=None)
+
+        mock_session_cls.return_value = mock_session
+
+        result = await client.process(
+            {
+                "model": models.image("lucy-pro-i2i"),
+                "prompt": "Add the object from the reference image",
+                "data": b"fake input image",
+                "reference_image": b"fake reference image",
+                "enhance_prompt": False,
+            }
+        )
+
+        assert result == b"fake image data"
+
+
 @pytest.mark.asyncio
 async def test_process_rejects_video_models() -> None:
     """Test that process() rejects video models with helpful error message."""