[rahulvohra]

For a while now, computers have been able to recognise human emotions more reliably than humans can: http://www.cl.cam.ac.uk/research/rainbow/emotions/

Given a good full frontal view of a face, a computer can tell the difference between laughing and crying or sadness and anger. The real challenge is dealing with variance in pose and lighting.

(Disclosure: I was doing a PhD in that research group.)