The sculptures of Shigeo Fukuda show that shadows and reflections (mpegs) may not be what they appear to be. When you turn M.C. Escher's drawings into sculptures, you can get some impossible objects (mpeg). And Dick Termes paintings on globes are stunning examples (Quicktime) of six point perspective. All of these works of illusionary art are featured in the book Masters of Deception: Escher, Dalí & the Artists of Optical Illusion and must be seen to be believed.