CAPTCHA
CAPTCHA stands for Completely Automated Public Turing test to tell Computers and Humans Apart. A CAPTCHA is typically presented as a graphic with distorted letters or numbers that a user must decipher and enter into a text field. Although CAPTCHA attempts to ensure a response that is generated by a person, nearly all modern CAPTCHAs can be readily solved by computer programs. Graphical CAPTCHAs cannot be made screen reader accessible. By their nature, CAPTCHA introduces usability, accessibility, and cognition issues for end users, and therefore should be avoided when possible. When necessary, audio CAPTCHA (distorted audio is played instead) should be provided in addition to a graphical CAPTCHA.