I'd like to create a dynamic thumbnail resizer so that you can use the following URL to get a resized image:

```
http://server/images/image.jpg?width=320&height=240

```

I tried setting up a route like this:

```
routes.MapRoute(null,
                "{filename}",
                new { controller = "Image", action = "Resize" });

```

But if the file exists at the URL, ASP.NET will bypass the routing and return you just the file instead. How do I force ASP.NET to route the images instead of returning what's on disk?