Optical illusions are great subject matter for tattoo designs. A common for is anamorphosis. Anamorphosis is technique that creates an optical illusion where hidden messages or hidden images can be revealed. When veiweing straight-on, the text or image is hidden and cannot be seen. When the viewer changes his position or view the artwork can be seen from a particular angle. At that angle is where the hidden text or image can be seen. It's a play on the eyes!