Try this http://www.soundstep.com/blog/experiments/jsdetection/
It's awesome, i wonder is possible to integrate C2? There a lot of ways to do with webcam like css filters, webGl effects, etc.!
This particular demo might not be possible, but you can use the webcam in C2 - have you tried the User Media object?
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Yes, i tested between sprite and user media, there no way to do a collision using motion detection via webcam, there a source that how it did for the demo.
http://www.adobe.com/devnet/html5/articles/javascript-motion-detection.html