The arrow of missing time

I just wanted to make arrows for flow on an image from a camera to see how it worked. It uses "cvGoodFeaturesToTrack" .  It is me moving a glass across the carpet and the biggest problem seems to be that the encoding in a web cam is s**t 4 brains.
It may be all that most people want, but it is not even a real scientific -like- interface. It does however work well enough to experiment with the methods and software.