Just like their standards for film content which result in the familiar ratings system (G, PG, PG-13, R, etc), the MPAA (Motion Picture Association of America) has rules for what you can and can't show in a movie poster. According to MPAA spokeswoman Gayle Osterberg, the big no-nos are "depictions of violence, blood, people in jeopardy, drugs, nudity, profanity, people in frightening situations, disturbing or frightening scenes."
Yet somehow, the evil geniuses of entertainment advertising keep finding new ways to disturb the moviegoing public with their posters -- without breaking the rules. The latest (and perhaps most egregious to date) example is the teaser for Hostel II, which if you're brave, you can check out after the jump:
Hostel II: the photographers either took a trip to their local butcher shop, or ... well, I don't want to know.
Below that is the poster for The Hills Have Eyes II, which the MPAA actually did reject.
Finally, the poster for Michael Winterbottom's Road to Guantanamo, which I suspect was rejected by the MPAA for, I'm going to guess, a variety of reasons.