With the help of photoshop. check out this link and the thread.
http://www.autoblog.com/photos/pixar-cars-photochops/
http://modularpowerhouse.com/forums/showthread.php?t=42184
http://www.autoblog.com/photos/pixar-cars-photochops/
http://modularpowerhouse.com/forums/showthread.php?t=42184