What is CAPTCHA and How it Works?

CAPTCHA or Captcha (pronounced as cap-ch-uh) which stands for “Completely Automated Public Turing test to tell Computers and Humans Apart” is a type of challenge-response test to ensure that the response is only generated by humans and not by a computer. In simple words, CAPTCHA is the word verification test that you will come across the end of a sign-up form while signing up for Gmail or Yahoo account. The following image shows the typical samples of CAPTCHA.