Fending off SPAM with reCAPTCHA

Posted on 10:49 PM by Rafael Minuesa

reCAPTCHA is a free CAPTCHA service that helps to digitize books, newspapers, magazines and all kinds of old publications that can only be found on a printed medium.


The term CAPTCHA stands for “Completely Automated Public Turing test to tell Computers and Humans Apart”, and is a type of challenge-response test used in computing to ensure that the response is generated by a human being. The process involves the use of software that displays some challenging inquiry that computers are unable to decipher. Or at least, that’s the goal. The most common type of CAPTCHA requires that the user type letters or digits from a distorted image that appears on the screen.

However, computers are getting smarter by the day and it’s gotten to the point where the images are being correctly guessed by newly developed software. To counteract these advancements  CAPTCHAS are being made even more difficult to read, with the end result of humans having a hard time trying to guess the correct answer, while spambot software is simply evolving and outperforming any effort to outsmart them by the very humans who designed them in the first place.

The line between what was readable to humans and unreadable to computers was about to be crossed in the wrong directions, when a new CAPTCHA approach named reCAPTCHA emerged from the work of Guatemalan computer scientist Luis von Ahn. An early CAPTCHA developer, von Ahn realized that “he had unwittingly created a system that was frittering away, in ten-second increments, millions of hours of a most precious resource: human brain cycles.”

About 200 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.


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