Captchas and crowdsourcing

What if… you can help 100 million people to learn a new language, and let them help translate the web in return?

Duolingo -- the next chapter in human computation Luis von Ahn TEDxCMU 2011 (Apr 26, 2011)

TEDxCMU — Luis von Ahn — Duolingo: The Next Chapter in Human Computation (by TEDxTalks)