Homography Matrix

 http://en.wikipedia.org/wiki/Homography

Homography is a concept in the mathematical science of geometry. A homography is an invertible transformation from a projective plane to a projective plane that maps straight lines to straight lines. Synonyms are collineation, projective transformation, and projectivity.^[1]

Computer vision applications

In the field of computer vision, any two images of the same planar surface in space are related by a homography (assuming a pinhole camera model). This has many practical applications, such as image rectification, image registration, or computation of camera motion—rotation and translation—between two images. Once camera rotation and translation have been extracted from an estimated homography matrix, this information may be used for navigation, or to insert models of 3D objects into an image or video, so that they are rendered with the correct perspective and appear to have been part of the original scene. (This is called Augmented Reality.)

If the camera motion between two images is pure rotation, with no translation, then the two images are related by a homography (assuming a pinhole camera model).