Street artist/illusionist Julian Beever creates unique artwork on city sidewalks. He uses a complex geometric arrangement resulting in images looking amazingly realistic and 3D, but only if viewed from one particular side of the drawing. Oddly, from any other vantage point the drawing looks deformed.
Check out the section titled “Anamorphic illusions drawn in a special distortion in order to create an impression of 3 dimensions when seen from one particular viewpoint” and enlarge the thumbnails at
http://users.skynet.be/J.Beever/pave.htm