CAPTCHA and ReCAPTCHA

4 10 2007

captchas

Here’s an acronym that’s bound to impress your friends: CAPTCHA. It stands for “Completely Automated Turing Test to Tell Computers and Humans Apart” (I’m not sure where the ‘P’ comes from). You might have come across a CAPTCHA the last time that you signed up for a free email account, joined Facebook, or purchased tickets to a concert.

A CAPTCHA is a small graphic that has distorted letters and numbers and it is designed to thwart spammers. Spammers often use bots (automated programs) to sign up for free accounts that can then be used to send that spam we love so much. CAPTCHAs make life more difficult for spammers because bots cannot easily recognize distorted letters and, therefore, cannot complete the sign in process for their free email accounts.

If you ask me, CAPTCHAs are ingenious – but ReCAPTCHAs are even better. Currently, there are large scale projects to scan old books (that are in the public domain) and make the text available online. When these books are scanned, the images are run through Optical Character Recognition (OCR) software so that that the content can be indexed. While OCR does a decent job recognizing words there are times when the character string is too convoluted for the software to decipher – and that’s where ReCAPTCHAs come in. These confusing sections of old texts are quickly decoded by internet users and the data that they input clarifies the text and contributes to the digitization projects. Popular websites like Facebook, Twitter and StumbleUpon use ReCAPTCHAs.

For more information on CAPTCHAs and using networks of human processing power to assist computers read this article from Wired about Luis Von Ahn (inventor of CAPTCHAs). Or, check out this story from BBC’s technology pages.

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One response

4 10 2007
mozey

that is a clever idea!,

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