Headswaps...
haven't tried one of those yet
(Pavlov'sDog Sit! Pavlov'sDog, Thu 16 Aug 2007, 14:42, archived)

all you need is a picture with two people looking in the same general direction
and the clone tool really

:)
(Slartibartfast. Is currently ignoring: Slartibartfast, Thu 16 Aug 2007, 14:49, archived)