Strictly speaking: anamorphosis

In classical Greek, anamorphosis meant “transformation”, and was first applied by Renaissance artists to a highly regarded technique of manipulating the perspective on an image. It presented an apparently distorted drawing of an object, which when seen reflected in a curved mirror, or from a particular angle, was well-proportioned and three-dimensional. But its later applications in 18th and 19th century English find it in negative territory: referring to the “deformation” of an image, and “degeneration” of a plant or a language to an earlier form (Oxford English Dictionary online).