Example of homography.
homography-example.pl image
Opens two image panes. The first pane is the image given as an argument and referred to as image1. The second image pane is a blank image referred to as image2. User can click four points on image1 to identify a planar surface. Then the user can click four points on image2 to specify where the four points from image1 should map. Program then computes homography matrix H and transforms image1.