CAPTCHA is short for "Completely Automated Public Turing test to tell Computers and Humans Apart."
It is the human being who has to prove that he is not a machine. That is why it is also known as the Turing Test.
CAPTCHA is an answer test prepared in such a way that only a human can enter the test characters into a distorted image and no computer can interpret them.
With more and more bots and crawlers flooding the internet, it is no longer a question of whether or not a CAPTCHA is required on a website.
EN 
DE 
FR 
ES