Those annoying Captcha codes? They are now helping transcribe the world's books!

Luis von Ahn is the guy who invented Captcha - that ubiquitous tool that prevents spammer bots flooding websites.

Addressing a TED conference in a funny and inspiring talk, he describes how he was initially proud to realise that 200 million Captchas are filled out every day world-wide. But then he stopped to think that each time took 10 seconds, so people were wasting 500,000 hours EVERY DAY filling them out!

He started thinking about ways those 10 second chunks could be turned to a useful task.






So now there are two "words" on each Captcha (oh yeah - so there are, you just thought to yourself). One is a Captcha as usual, and the other an actual word from a book that their system didn't recognise. If you get the Captcha right, it assumes you are human and that there is some confidence you got the other word right too. If several people get the same answer for that word, then bingo, they have that word digitised accurately.

Now there are 350,000 sites using this new ReCaptcha system. All up this means that about 100 million words a day are being transcribed, or some 2.5 million books a year!

The rest of the talk is about new projects he is turning the system to - problems broken up into 100 million tiny chunks.