reCAPTCHA

reCAPTCHA is a common security feature on web pages used to distinguish human users from automated bots. reCAPTCHA appears as a small dialogue or popup on a website asking the user to perform a simple tasks such as read text or match images. The tasks are designed to be simple for humans, but hard for machines, hence useful to distinguish then, indeed the term CAPTCHA is originally an acronym for "Completely Automated Public Turing test to tell Computers and Humans Apart". While this is their primary purpose, they are also used to fill in gaps in AI algorithms and to create labelled training data for machine learning. The original reCAPTCHA helped fill in difficult portions of OCR for scanned books and is an early example of human computation.

Used on pages 408, 453

Also known as recaptcha codes