When an image is viewed in a mirror which is not flat, the image appears distorted and is a mirror anamorph. A familiar example is the common right-hand rear-view-mirror on many automobiles that provide an expanded but distorted view. Another familiar example is the FUNHOUSE MIRROR in which the distortions are carried to comic extremes.
Courtesy of Givens Designs Inc., http://www.givensinc.com/mirror.html

Beginning in the renaissance, artists experimented with the anamorphic images produced by simple mirrors. Of the many possibilities, the conical mirror and the cylindrical mirror were the most common. Because conical mirrors are difficult to make and cylindrical ones are easy the cylindrical anamorph is the most common.
This is a cylindrical anamorphic painting by an unknown artist of Nicholas Lancret's "Par un Tendre Chansonnette" (With a tender little song). Its reconstruction in a cylindrical mirror is shown below.

The image is reconstructed in the cylindrical mirror. The image plane in the mirror has a peculiar shape-it is nearer the front of the mirror at the base and recedes to the centre higher up. This gives the image a certain three dimensional quality not found in other plane images. 
These anamorphs were valued decorations among the wealthy, particularly in the 17th and 18th centuries. Many famous paintings were copied as anamorphs for the aristocracy. In the 19th century, with the transfer of interest to photography, the cylindrical anamorph became a children's toy.