anamorphoscope

from The Century Dictionary.

• noun An optical toy consisting of a vertical cylindrical mirror which gives a correct image of a distorted picture drawn at the base on a plane at right angles to the axis of the mirror. See anamorphosis.

from the GNU version of the Collaborative International Dictionary of English.

• noun An instrument for restoring a picture or image distorted by anamorphosis to its normal proportions. It usually consists of a cylindrical mirror.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A mirrored device which gives a correct image of an anamorphosis.