Anamorphosis is a distorted projection or perspective requiring the viewer to occupy a specific vantage point, use special devices or both to view a recognizable image. Some of the media it is used in are painting, photography, sculpture and installation, toys, and film special effects. The word "anamorphosis" is derived from the Greek prefix ana‑, meaning "back" or "again", and the word morphe, meaning "shape" or "form". An oblique anamorphism is the visualization of a mathematical operation called an affine transformation. The process of extreme anamorphosis has been used by artists to disguise caricatures, erotic and scatological scenes, and other furtive images from a casual viewer, while revealing an undistorted image to the knowledgeable spectator.