diff --git a/src/mcp_synology_container/modules/images.py b/src/mcp_synology_container/modules/images.py
index b4f3c5b..254f900 100644
--- a/src/mcp_synology_container/modules/images.py
+++ b/src/mcp_synology_container/modules/images.py
@@ -166,9 +166,13 @@ def register_images(mcp: FastMCP, config: AppConfig, client: DsmClient) -> None:
             confirmed: Must be True to actually delete. Default False shows
                        a preview only.
         """
-        # Parse name:tag
-        name, _, tag = image_id.partition(":")
-        if not tag:
+        # Parse name and tag using the last ":" as separator so that
+        # registry-prefixed images (e.g. "ghcr.io/foo/bar:v1") are handled
+        # correctly.  rpartition returns ("", "", original) when ":" is absent.
+        name, sep, tag = image_id.rpartition(":")
+        if not sep:
+            # No ":" found — bare name without explicit tag
+            name = image_id
             tag = "latest"
 
         # Fetch the local image list for size reporting and in-use detection
diff --git a/tests/test_modules/test_images.py b/tests/test_modules/test_images.py
index 005969a..944f187 100644
--- a/tests/test_modules/test_images.py
+++ b/tests/test_modules/test_images.py
@@ -291,6 +291,52 @@ async def test_delete_image_by_hash():
     assert "redis" in result
 
 
+@pytest.mark.asyncio
+async def test_delete_image_registry_prefixed_name():
+    """Registry-prefixed image names (e.g. ghcr.io/foo/bar:v1) must split at last ':'."""
+    from mcp_synology_container.modules.images import register_images
+
+    registry_images = {
+        "images": [
+            {
+                "id": "sha256:dddd",
+                "repository": "ghcr.io/open-webui/open-webui",
+                "tags": ["v0.8.10"],
+                "size": 100 * 1024 * 1024,
+                "created": 1700000000,
+                "upgradable": False,
+            }
+        ]
+    }
+
+    client = AsyncMock()
+
+    async def mock_request(api, method, **kwargs):
+        if api == "SYNO.Docker.Image" and method == "list":
+            return registry_images
+        if api == "SYNO.Docker.Container":
+            return {"containers": []}
+        if api == "SYNO.Docker.Image" and method == "delete":
+            return {}
+        return {}
+
+    client.request.side_effect = mock_request
+    mcp, tools = make_mock_mcp()
+    register_images(mcp, make_config(), client)
+
+    result = await tools["delete_image"](
+        image_id="ghcr.io/open-webui/open-webui:v0.8.10", confirmed=True
+    )
+    assert "Deleted" in result
+    assert "open-webui" in result
+
+    # Verify delete was called with correct split params (not "ghcr" as name)
+    delete_call = next(c for c in client.request.call_args_list if c.args[1] == "delete")
+    params = delete_call.kwargs.get("params") or {}
+    assert params.get("name") == "ghcr.io/open-webui/open-webui"
+    assert params.get("tag") == "v0.8.10"
+
+
 @pytest.mark.asyncio
 async def test_delete_image_api_error():
     from mcp_synology_container.dsm_client import SynologyError