Digitizing Books While Fighting Spam

You may have noticed that I recently added a CAPTCHA to my blog. My blog was getting flogged by spam comments that were making it past my Akismet Spam filter. I decided to install the reCAPTCHA wordpress plugin.


ReCAPTCHA is a system developed at Carnegie Mellon University that uses CAPTCHAs to digitize scanned books! The plugin will give you 2 words to verify that you are a human and can in fact identify the words correctly.

How does it 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.

Source: http://recaptcha.net/learnmore.htmlÂ

I believe this is innovation at its finest. The guys and gals over there at Carnegie Mellon should really be commended for this effort.

If you post a comment, you can feel good about contributing to a greater good.

3 thoughts on “Digitizing Books While Fighting Spam”

  1. I just wanted to see how it worked so I’m leaving a comment. Nifty. I like how it has stuff for disabled people as well such as audio captcha. I am disappointed however, that the audio doesn’t use a built in medium and requires Quicktime. Still a neat concept.

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