This is dumb. A hash? That's only going to deter the most incompetent internet users when it comes to a file type that is subject to alteration without losing it's information value (pictures, video, music, etc.).

All someone has to do is change a single bit/pixel in the image and the hash will be different. No one will notice that and it defeats the hash. Hell, you don't even have to do that. You can just rotate the image, save it, then rotate it back, and re-save it. The odds are that program that you used will most certainly not write the image data in the same exact way.

Hashes would be better for files that cannot be altered without breaking the contents. Although, these could be subject to compression, which would create a new hash.

Either way, I think they need to use something similar to Google's image search that actually examines the photo contents for similarity.