Simple, noisy, skin detection in the browser, see <a href="skin-detection/">skin-detection</a> (note that you'll need 
a browser which supports <a href="http://timtaubert.de/blog/2013/02/getusermedia-part-3-simple-motion-detection-in-a-live-video/">getUserMedia()</a>).

Some history of why I did this is 
<a href="http://blog.houseofmoran.com/post/70835570249/playing-music-when-someone-is-typing">on my blog</a>.