This is a very neat idea. A couple of questions come to mind:

Do you rely on an outside source for picture identification? If so, what's your plan if/when it fails? If not, do you plan to build your own in-house system?

Have you tested whether your code has any impact in page load speed (Y-Slow and company)?

Related to Q1, if you have your own in-house system, will you have your own database of pictures for feature extraction/matching, and how do you plan to make it large enough (and grow it fast enough) to accomodate the wide variety of pictures that people take and post?

I think that if you implement this well, you potentially have a real winner here. Best of luck to you!