Stereoscopy (SOURCE - WIKIPEDIA)

Stereoscopy (also called stereoscopic or 3-D imaging) is any technique capable of recording three-dimensional visual information or creating the illusion of depth in an image.
Human vision uses several cues to determine relative depths in a perceived scene. Some of these cues are:

• Stereopsis
• Accommodation of the eyeball (eyeball focus)
• Occlusion of one object by another
• Subtended visual angle of an object of known size
• Linear perspective (convergence of parallel edges)
• Vertical position (objects higher in the scene generally tend to be perceived as further away)
• Haze, desaturation, and a shift to bluishness
• Change in size of textured pattern detail

All the above cues, with the exception of the first two, are present in traditional two-dimensional images such as paintings, photographs, and television. Stereoscopy is the enhancement of the illusion of depth in a photograph, movie, or other two-dimensional image by presenting a slightly different image to each eye, and thereby adding the first of these cues (stereopsis) as well. It is important to note that the second cue is still not satisfied and therefore the illusion of depth is incomplete.
Many 3D displays use this method to convey images. It was first invented by Sir Charles Wheatstone in 1838. Stereoscopy is used in photogrammetry and also for entertainment through the production of stereograms. Stereoscopy is useful in viewing images rendered from large multi-dimensional data sets such as are produced by experimental data. Modern industrial three dimensional photography may use 3D scanners to detect and record 3 dimensional information. The three-dimensional depth information can be reconstructed from two images using a computer by corresponding the pixels in the left and right images (e.g.,). Solving the Correspondence problem in the field of Computer Vision aims to create meaningful depth information from two images.