You know I had thought of a similar idea a while back, when I heard video game producers were doing this to stop pirated leaks of beta's given to hardware/software companies.
I forget who it was, but one of the major game producers was adding in hidden ID's to each beta they gave out to help track down whom was pirating their games.
I was thinking some sort of unique id added to each picture and video would let you track down a member id of whom ever stole the content. Programs could then black list these users if they shared data bases with each other.
I'm really surprised no one has ever done this and congrats for actually doing it. If I were you, I'd add a way to do this to pictures as well so you have a complete system. You should be able to make some decent money licensing it to various content producers and programs if it works well.
