I think hashing pictures and storing the results to compare with future uploads is a perfectly reasonable thing to do. This is the same thing that is done with CP pictures and for much the same reason.<p>The only thing that makes me nervous is the actual uploading of pictures in order to be scanned. It should be possible to create a client-side image processor that generates the appropriate hash but doesn't involve uploading your pictures to a server somewhere. Perhaps a Javascript processor in-browser or even a native desktop app.
@dang, can we get the title changed for this story? The original was "Facebook’s testing a new method to prevent revenge porn that requires uploading your nudes" which seems more descriptive and helpful.