captcha means Completely Automated Public Turing test to tell Computers and Humans Apart.
A captcha is a test to prove that the person submitting a form is a human and not a bot.
They are explicitly designed to prevent automation.
A captcha occurs when the contact is asked to resolve a challenge:
A captcha test is also difficult for human and is therefore a barrier on forms submission
recaptcha is easier.
Simpler than captcha
Captcha is explicitly designed to prevent automation and there are two primary strategies to get around CAPTCHA checks: