title: Find Different area between two images
body: <p>My purpose is to compare pixels between two images and find out minimal(optimized)
  rectangular area that contains all different pixels between images.
  Simply, I compared all pixels(for example 1024*768 pixels) of two images and found out different part ,but it is not good idea because of speed.
  I need to do this compare at least fifteen times per second.
  Do you know any more effective algorithms for it?</p>