It is a method to check if you are really interacting with a human and not with a machine, also the image or audio that is used for the test. As an acronym it is taken from the English phrase Completely automated public Turing test to tell computers and humans apart, which is precisely based on the Turing test to confirm if we would be able to recognize when we are dialoguing with a person or with an artificial intelligence. For this case the usual thing is to present publicly the image of a distorted text, which can not be interpreted by the OCR scanner of an AI but by a person, so it is also called "Inverse Turing", since the original test referred to recognizing a machine that simulates being human. See recaptcha, Voight-Kampf.
CAPTCHA or CAPTCHA stands for Completely Automated Public Turing test to tell Computers and Humans Apart (Turing test public and automatically to differentiate human ) and machines. This test is controlled by a machine, rather than by a human as in the Turing test, for it consists of a reverse Turing test.This is a test challenge-response used in computing to determine when the user is or not human. The term was first used in 2000 by Luis von Ahn, Manuel Blum and Nicholas J. Hopper of the University Carnegie Mellon, and John Langford of IBM. It consists of the user to correctly enter a set of characters that are displayed in a distorted image that appears on the screen. Assumes that a machine is not able to understand and enter the sequence correctly so that only the human could do it.
