Developer tools Digitisation Web 2.0

Stop spam and help correct OCR errors – at the same time!

reCaptcha is a nifty project that uses the now familiar ‘Captcha’ web form spam prevention technique to help fix OCR problems in global digitisation projects.

Currently this great example of socially responsible crowdsourcing is helping fix digitisation errors and inconsistencies in books scanned for the Internet Archive – books that will be reproduced in the developing world through projects like the Million Book Project.

If you are considering (or already use) a Captcha tool on your website or blog you might consider swapping over to reCaptcha so that your users, when submitting comments, aren’t just keeping your site free of spam but they are also helping fix digitisation for others.

There are downloadable plugins for WordPress, mediaWiki, PHPbb, as well as a general PHP class, and a range of APIs to choose from for easy implementation in projects.

Here’s the project blurb –

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.

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.