Aha! Your reference cited in Footnote 5 that there was a way to distinguish human skin and that it fell into a narrow range. I found the article referenced in that footnote:
http://repository.upenn.edu/cgi/view...ext=cis_papers
They found that using RGB values was a poor way to identify human skin and instead used skin spectograph data which measures the reflectance of light off of skin. Turns out that human skin has some unique qualities there, which are not affected by the color of one's skin. Thus their process doesn't even bother with collecting or analyzing skin color, but just the reflective properties of surfaces within a narrow band of light, a "wavelet."
They found that their process had a very high success rate in distinguishing human skin from that of a mannequin having the same color surface as human skin, based upon the unique reflectivity properties of human skin. Very technical & interesting research. It doesn't say how quickly this data could be collected and analyzed, so I don't know if this method could be used for real-time monitoring of computer screens.