I can only imagine that this would just make the photos unusable (I imagine a "John Smith" printed diagonally on a photo, enough to make it 'viewable' by friends, but unusable by advertisers. Of course there is always photoshop, and I will assume that even if someone watermarks a photo like that, someone, somewhere can spend 10mins and process/edit the semi-transparent letters so as to 'remove' them from the picture.