If the user normally encounters photos on the site by requesting them (e.g., by entering a search query or browsing a friend's album) rather than having random photos thrown in their face (like HotOrNot.com), I would think you could run into some very upset users (and possibly legal problems) if you are throwing random photos that might contain disturbing images in their faces. I mean, if you go to a website intending to browse photos your friend took of his boat and the site throws up some random child porn on your screen, you'd be pretty annoyed, right?