From Scratch with Jessica Harris Luis von Ahn
Oct 17, 2025
Luis von Ahn, inventor of CAPTCHA and founder of Duolingo, talks about launching his startups, his childhood fascination with computers, raising venture capital, and his current exercise routine in an entertaining interview with Jessica Harris.
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CAPTCHA As A Computer-Judge Turing Test
- CAPTCHA is a computer-judge version of the Turing test that asks if the user is human rather than if the machine is intelligent.
- Luis von Ahn explains the paradox that a computer must reliably detect humans while remaining hard for machines to solve.
Turn Play Into Productive Work
- Games With A Purpose (GWAPs) capture human effort on tasks computers struggle with by making them fun.
- Von Ahn turned crowdsourced leisure activities like crosswords into useful computation through playful tasks.
Wasteful CAPTCHA Taps Became ReCAPTCHA
- Von Ahn calculated people typed CAPTCHAs ~200 million times daily, wasting about ten seconds each time.
- He repurposed that human effort into ReCAPTCHA to help digitize words OCR couldn't read.
Luis is an inventor and computer science professor at