Anamorphic Eye
One form of anamorphosis involves a deformed image that is painted on a flat surface, such as a sheet of paper. When a cylindrical (or sometimes conical) mirror is placed in the appropriate spot, the deformed image is suddenly transformed into something recognizable.
In the example above by Hungarian artist István Orosz, a human eye and eye brow can be easily identified. Without the mirror, however, it is difficult to tell exactly what the drawing on the paper represents.