On reCaptcha

My interest in CAPTCHAS never seems to vane. And now theres reCAPTCHA!! And its very interesting to understand how its put to use.

It is estimated that around 60 million captchas are solved every day, each involving around 10 seconds. That roughly translates into 170,000 hours of work! Those are some astounding figures. The essential idea behind ReCaptcha is to constructively channelise this huge amount of work.

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.

This cool feature can be added to your website/blog, as also in the form of MailHide to mask your email id, thus helping the cause of digitizing valuable knowledge.