Also found in: Dictionary, Medical, Wikipedia.


A method for soliciting help from the general public in order to assist large, text-to-computer projects that digitize thousands of old books. Regular CAPTCHAs are the distorted words found on websites that users type back in to validate that they are humans and not computers. Every day, hundreds of millions of CAPTCHAs are entered, creating a huge pool of human resources to draw from.

In a reCAPTCHA system, the images of words that the optical character recognition (OCR) program cannot decipher are dispersed to several people in the form of a CAPTCHA to get a consensus. Originally developed by Carnegie Mellon University, reCAPTCHA was acquired by Google in 2009. For more information or to get reCAPTCHA code, visit See OCR and CAPTCHA.

A known word (left) is always sent with the bad word so that the reCAPTCHA serves as a valid CAPTCHA. After several people enter the same text for the bad word, the system considers the word properly converted.

In 2014, Google introduced No CAPTCHA human authentication. Most of the time, users only have to click the box. If the system fails to authenticate, a test is presented such as having to select all the animal pictures from a group that are the same species as the given image.
Copyright © 1981-2019 by The Computer Language Company Inc. All Rights reserved. THIS DEFINITION IS FOR PERSONAL USE ONLY. All other reproduction is strictly prohibited without permission from the publisher.
References in periodicals archive ?
When asked why Nest does not use ReCaptcha, Sathe cited difficulty in implementing it on mobile apps, and user convenience.
Many were also surprised to see a reCAPTCHA feature that was introduced on the login pages over the weekend.
Four years ago, Google turned reCAPTCHA into a system for training AI
But such a task can also be completed by relying on crowdsourcing, through the reCAPTCHA application.
Reference [30] trained large, distributed deep convolutional neural networks and achieved 99.8% accuracy in recognizing CAPTCHA images of reCAPTCHA.
In addition to security issue, a recent research pointed out that existing schemes of CAPTCHA, including reCAPTCHA, are not appropriate for mobile devices.
Next, in 2007 reCAPTCHA, originated by Luis Von Ahn.
(438) Similarly, the reCAPTCHA security feature on many Web registration forms, in which users type words appearing in an image, is actually part of a worldwide effort to digitize books and other content.
The workshop brought together 31 attendees from industry and academia, with a strong representation from universities (42 percent of the attendees), the largest crowdsourcing customers like Google, Microsoft, and Xerox (39 percent of the attendees), and the leading crowdsourcing platforms like Amazon's Mechanical Turk, CrowdFlower, Galaxyzoo, reCAPTCHA, and Mobile-works (19 percent of the attendees).
William Eggers' praise for Luis von Ahn's reCAPTCHA idea overlooks one vexing problem ("Crowdsourcing Social Problems," January).