CAPTCHA
CAPTCHA , an acronym for "Completely Automated Public Turing Test to Tell Computers and Humans Apart," refers to various authentication methods that validate users as humans, and not bots, by testing users with a challenge that is simple for humans but difficult for machines. CAPTCHAs prevent scammers and spammers from using bots to fill out web forms for malicious purposes. The term CAPTCHA was coined in 2003 by a group of computer science researchers at Carnegie Mellon University led by Luis von Ahn and Manuel Blum. Launched by von Ahn in 2007, reCAPTCHA v1 had a dual aim: To make the text-based CAPTCHA challenge more difficult for bots to crack, and to improve the accuracy of optical character recognition (OCR) being used at the time to digitize printed texts. In 2009, Google acquired reCAPTCHA and began using it to digitize texts for Google Books while offering it as a service to other organizations. According to Google , every time its CAPTCHAs are solved, that human e