came across these via a forward mass mail thing about the pavement artwork of a UK dude by the name of julian beever - "anamorphic illusions drawn in a special distortion in order to create an impression of 3 dimensions when seen from one particular viewpoint"
here's a shot of what one of his pieces look like from the "wrong" angle:
and now looking at it from the intended perspective:
more pictures at http://users.skynet.be/J.Beever/pave.htm
pretty nifty, eh? makes you wonder whether sometimes you just can't seem to understand certain things, it's because you're standing on the wrong side of the picture...