Originally Posted by Gucci Little Piggy

Well that's a start. I'd say the upper left would be fairly easy, and the one to the left of Björk wouln't be too hard either. Those who know and recognize the lower right one, however, must be some sort of demi-gods.

E: Oh, I only now realise that this format cuts the pictures off, sometimes leading to confusing situations. Here's one of them in its full (because nobody would be able to guess it like this):