Researchers at the University of Liege in Belgium have made a breakthrough in machine vision. Background extraction is the separation of a "normal" background image from more interesting "new" pixels such as moving objects.
This new algorithm is very high performance and computationally efficient. Unfortunately, it's completely patented, but a demo video and a paper describing the method are linked below.
O. Barnich and M. Van Droogenbroeck. ViBe: a powerful random technique to estimate the background in video sequences. In International Conference on Acoustics, Speech, and Signal Processing (ICASSP 2009), pages 945-948, April 2009. Available as a IEEE publication or on the University site.