For those who may not be knowledgeable, a Captcha is a form of challenge-response examination used to conclude whether the entity is a person or a computer. The conventional Captcha often consists of a series of visuals or symbols that the user must decipher and input into a text area. The goal is to validate that the entity is a being and not a script trying to enter a site or service.
The Evolution of Captcha
The Endless Captcha Game: A Perpetual Battle Between Humans and Scripts Infinite Captcha Game
The Development of Captcha