More explanation for motion detection algorithm

[chfakht]

The file alg.c contain the algorithm used for motionDetection in a video stream. However this page http://www.lavrsen.dk/foswiki/bin/view/Motion/MotionTechnology haven't explain a lot about it and the source code is very long (>1000 lines)
So i'm looking for further explanation or further reading from other sources to learn it and understand it

Many thanks