Video CAPTCHAs: Usability vs. Security
Kurt Alfred Kluever, Richard Zanibbi · RIT Scholar Works (Rochester Institute of Technology) · 2008
A Completely Automated Public Turing test to tell Computer and Humans Apart (CAPTCHA) is a variation of the Turing test, in which a challenge is used to distinguish humans from computers (‘bots’) on the internet. They are commonly used to prevent the abuse of online services; for example, malicious users have written automated programs that signup for thousands of free email accounts and send SPAM messages. A number