Ten Seconds, Two Hundred Million Times a Day
Luis von Ahn was born in Guatemala City in 1978. His mother, a physician, bought him a computer when he was eight. He came to the United States for university and earned a PhD in computer science at Carnegie Mellon, where he later became a professor.
Around 2000, von Ahn and colleagues developed the CAPTCHA: a challenge that separates humans from automated programs, or bots, by exploiting a gap between what people find easy and what software finds hard. The distorted-text CAPTCHA became standard equipment across the web, blocking bots from mass-registering fake accounts.
Von Ahn then made a second, sharper observation. Roughly 200 million CAPTCHAs were being solved every day, each taking about ten seconds. That was an enormous amount of human effort producing nothing but a gate check. His answer was reCAPTCHA: show the user one word the computer already knew and one word that had defeated OCR software while scanning old books and newspapers. The known word verified the human; the unknown word got transcribed for free. Google acquired reCAPTCHA in 2009.
He calls this idea human computation — designing systems where routine human effort, aggregated at enormous scale, solves problems computers cannot. In 2011 he applied it again by co-founding Duolingo with Severin Hacker, building a free language-learning platform now used by hundreds of millions of people.
