Markus Krause and Jan Smeddinck of Bremen University have written a useful survey about human computation games, where users are asked to solve hard problems while participating to simple digital games. A paradigmatic example is “ESP”, in which users are asked to tag images and get a reward when two users adopt the same label at the same time. In 2006, ESP has been licensed to Google to classify images and offer a better service to Google Images Search users: a good demonstration of the effectiveness of online Human Computation Games, and a proof that today there is an infinite number of ways of putting people at work. Since then, a lot has been done and written about such peculiar crowdsourcing technique. The paper of Krause and Smeddinck offer a great chance to those who missed this field and would like to recover promptly. You will find it published in the proceedings of the EUSIPCO 2011 conference.