The website Being John Malkovich - ECCV 2010 demonstrates software called PhototBios that allows you to control another person's face as if they were a puppet. It works by creating a large collection of photographs of the person you want tp be the puppet. These photographs should be from as a large number of angles and variety of expressions as possible.
The puppeteers face is then mapped and when, in front of a webcam, they move their heads and change their expressions face recognition is used to select the appropriate image of the puppet and display it. There are morphing algorithms to smooth the transition between pictures to create a cleaner animation of the puppet.
Very cool, yet very creepy at the same time because the puppet's pictures can be grabbed of a video or large collection of photographs without the eventual puppet's knowledge. Much opportunity for Eeevil hi-jinx if you ask me.