Completely Automated Public Turing (test for telling) Computers and Humans Apart. n. A test designed to determine whether a user is human or a spam bot, often consisting of a sequence of obscured graphic letters or numbers that must be typed into a field to continue. Some visually impaired individuals have difficulty reading captchas and spammers are continually developing successful methods of subverting the scheme. [Coined in 2000 by Luis von Ahn, Manuel Blum, and Nicholas J. Hopper of Carnegie Mellon University and John Langford of IBM.]