The problem with your solution is that it requires cooperation; If I'm running a competitor of facebook, (and a dating site, in a way, is a competitor to faceb

The problem with your solution is that it requires cooperation; If I'm running a competitor of facebook, (and a dating site, in a way, is a competitor to facebook) I'm not going to want to just give them my content, you know? You'd be better off with something like tineye or google image search; something that snarfs all the photos off the web, you know, does this regularly and timestamps where it saw the photo first. It wouldn't be 100% but would likely work better than the cooperative solution you propose, and it's something that is well within the capabilities of facebook. Even then... yeah, I think this sort of thing is going to be pretty much impossible to completely stamp out as long as you can sell fake profiles for enough money that you can pay an actual human to create them.