Or I photoshopped it enough that your filter can't see it is the same and therefore it is now mine (this is easier than you think).

Also images uploaded on Facebook aren't public by default, so tinyeye etc wouldn't have them.

Oh sorry, I misunderstood... Yes that could work, but you'd have to rely on all the big companies using it too. Getting something like Match.com to use it sounds like quite a challenge :)