A Perspective on Perspective
Here are some awesome pictures of a sidewalk artist drawing in perspective. Double perspective. He draws the images in perspective of his viewers so that the images look in perspective to a relative plane. Its pretty crazy stuff and best explained by just looking at them.
His artwork is so realistic and perfectly in perspective with the perspective of the camera I had to look twice when I was first looking at the images. In some of them, it was hard to believe it is sidewalk chalk and not sculptures and statues in the ground.
Trompe l’Oeil
Celeste has an article with a link to some interesting trompe l’oeil — or eye tricks.