Completely Automated Public Turing Test to Tell Computers and Humans Apart is more commonly referred to by its acronym, CAPTCHA. It is a type of challenge-response test used in computing to determine whether a user is a human or a machine. Websites use CAPTCHA to prevent spam and automated extraction of data. Because computers are unable to distinguish letters and numbers within moving or distorted images, CAPTCHA typically requires a user to enter letters or numbers presented in a visually distorted field.
The CAPTCHA method of identification has received many criticisms because the distorted letters are difficult to read and the process slows people down. However, Google’s new product reCAPTCHA authenticates human users with a click of a box, and other easier challenge-response tests are sure to follow.