Felice Varini perfects the art of large scale optical illusion. His perspective-localized paintings create the illusions of three-dimensional shapes floating in space...but they're actually just graphics painted on to the walls and structures that they seem to be floating against. His technique is one of anamorphosis, a distorted projection or perspective requiring the viewer to use special devices or occupy a specific vantage point to reconstitute the image.

Anamorphis sounds complicated, but it's best illustrated by Varini's work: