From the department of clever

I was listening to the ABC Book Show and Ramona started talking about anti-spam technology – which rather surprised me. She was interviewing Luis von Ahn who created CAPTCHA who had now produced reCAPTCHA. You know those nasty little visual quizes you fill out to prove to some computer that you are a human, and not a robot filling in their form.

Well Luis von Ahn refleced on the tens of millions of people each day who were spending ten seconds exercising their human intelligence to fill out forms and wondered if he could get them to spend that time more usefully. No problem. Here’s how it’s explained on the re-CAPCHA website.

About 60 million CAPTCHAs are solved by humans around the world every day. In each case, roughly ten seconds of human time are being spent. Individually, that’s not a lot of time, but in aggregate these little puzzles consume more than 150,000 hours of work each day. What if we could make positive use of this human effort? reCAPTCHA does exactly that by channeling the effort spent solving CAPTCHAs online into “reading” books.

To archive human knowledge and to make information more accessible to the world, multiple projects are currently digitizing physical books that were written before the computer age. The book pages are being photographically scanned, and then, to make them searchable, transformed into text using “Optical Character Recognition” (OCR). The transformation into text is useful because scanning a book produces images, which are difficult to store on small devices, expensive to download, and cannot be searched. The problem is that OCR is not perfect.

Example of OCR errors

reCAPTCHA improves the process of digitizing books by sending words that cannot be read by computers to the Web in the form of CAPTCHAs for humans to decipher. More specifically, each word that cannot be read correctly by OCR is placed on an image and used as a CAPTCHA. This is possible because most OCR programs alert you when a word cannot be read correctly.

But if a computer can’t read such a CAPTCHA, how does the system know the correct answer to the puzzle? Here’s how: Each new word that cannot be read correctly by OCR is given to a user in conjunction with another word for which the answer is already known. The user is then asked to read both words. If they solve the one for which the answer is known, the system assumes their answer is correct for the new one. The system then gives the new image to a number of other people to determine, with higher confidence, whether the original answer was correct.

Luis von Ahn gave numbers bigger than the one’s quoted above and said that re-CAPTCHA was now processing 5 million words a week (or perhaps it was per day), and doing the work some large number of people.

Verily it is amazifying.

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The Worst of Perth
16 years ago

I work for Curtin Uiversity in Perth. You should see what OCR does to the word Curtin.

Andrew Reynolds
16 years ago

Try working for one of the firms with an ALL CAPS acronym as a name.