Neat: "FLARToolkit will detect the marker from input image and calculate the camera position in the three dimension space."

example 1 example 2

Persist's book has as2 code that checks pixel color for web cam pixels (every sixth), a tracking solution that blew me away. It does not seem is a big leap to this.. but maybe it is?

I did an experiment with this a while ago. I'll post a link when it's readily available. Very cool framework though.