Anamorphosis is a distorted projection or perspective requiring the viewer to use special devices or occupy a specific vantage point to reconstitute the image. The word "anamorphosis" is derived from the Greek prefix ana-, meaning back or again, and the word morphe, meaning shape or form.More details at Wikipedia, which also has pictures of other anamorphic illustrations, and a link to a commercially-available toy you can purchase to make your own.
There are two main types of anamorphosis: perspective (oblique) and mirror (catoptric). Examples of perspectival anamorphosis date to the early Renaissance (fifteenth century). Examples of mirror anamorphosis were first created in the late Renaissance (sixteenth century).