EDIT - If no one objects, I'm going to highly recommend a self-enforced 'rule' (that is, it'll be the responsibility of the person who posted the picture to enforce it) that limits how long the guessing can go on. Nothing kills this game faster than when a game can't be guessed. Having said that, I'll just arbitrarily set the limit to 24 hours (ie: if no one guesses correctly in that time, I'll post the name of the game and just post something else, or pass things off to someone else who's interested).