Yes, I tested it too and it's very nice! It finds images with differences in color, and even superposed text, etc, just as promised in the video. Amazing, really.

Maybe it calculates some kind of hash on every image, an then it looks for images that are at a distance lower than n to such hash? But I don't know any hashing system for images that could work this way... could anyone explain?

Edit: a fingerprint is mentioned in the video, so I guess there is some kind of hashing system after all.