We're a startup from Poland and we created an image recognition API. You can test it for free and it would be awesome if you could give us your feedback.
You can find our API at: www.recognize.im
An example of what you can do with it: http://www.youtube.com/watch?v=K57Q-LVE1XU
If you are interested in testing, please send me a PM or submit your email address at our homepage.
We don't have the sample code for Windows Phone (for now), but our API is really easy to use so it shouldn't be a big problem for developers.