Phantograms, also known as Phantaglyphs, Op-Ups, free-standing anaglyphs, levitated images, and book anaglyphs, are a form of optical illusion. Phantograms use perspectival anamorphosis to produce a 2D image that is distorted in a particular way so as to appear, to a viewer at a particular vantage point, three-dimensional, standing above or recessed into a flat surface. The illusion of depth and perspective is heightened by stereoscopy techniques; a combination of two images, most typically but not necessarily an anaglyph (color filtered stereo image). With common (red–cyan) 3D glasses, the viewer's vision is segregated so that each eye sees a different image.
Phantograms can be created using drawn images, photographs, or computer-generated images. Phantograms are usually placed horizontally and are intended to be viewed standing back from the image, though they can also be placed vertically and viewed at an angle from above or below.