Even though the post was from 2008 I responded because I see this question being asked over and over again on various message boards and forums. I think it is a state specific issue. Some contend that posting pictures is a tortious invasion of privacy by the public display of private fact...
I personally consulted with a criminal defense attorney regarding this situation. In the state of Pennsylvania a person has done nothing criminal posting pictures. They person could sue you civilly, however they would need to prove or show that they suffered a financial loss due to the posting...