If we are talking about professional actors trying to trick the tracker, then yes, it should be pretty hard to design software to overcome it. But most people aren't that good, and although they can mislead their friends or collegues, they still leave clues to detect a fake emotion. If you are interested, Paul Ekman has quite a lot of literature on the topic, e.g. see [1].

[1]: http://www.ekmaninternational.com/paul-ekman-international-p...