There is no actual depth in the artwork so the artist must understand, at least intuitively, what information is in the environment that allow us to perceive depth. These sources of information are commonly called depth or distance cues . A consequence of the two-dimensional nature of painting and drawing is that we lose all the depth information that comes from the fact that we have two eyes. These binocular , or two-eye, depth cues require true depth and thus we will not discuss them in context with paintings or drawings. For example, there is the binocular depth cue called disparity .
Disparity arises from the fact that our two eyes have a slightly different view of the world.
To allow you to see disparity requires either real depth or two images developed as if from different positions like our eyes. This latter approach is illustrated in the photograph from the California Museum of Art. The person is looking at a slide with two images, much like a viewmaster, with each image being taken from a slightly different position to allow the brain to see disparity and, thus, see a very realistic three-dimensional picture. They were created by Peter Chang and Gareth Richards in England. There are actually two sets of random dots overlayed on these images, one for each eye.