It's still a bias, before and after photos are a notorious example.
http://www.t-nation.com/readArticle.do?id=460898
photos taken five minutes apart....
"Okay, so maybe you noticed the dates on the side of the film. The truth is, the before pics were taken about 5 minutes before the after pics, or as long as it took Davin to change his shorts, put up a different background, and readjust the lighting. "
Which guy do you prefer???