Captcha is the best way to avoid spamming your SignUp, Comments, Email and many other things that takes user input. What is Captcha? It is a simple text combination of some uppercase and lowercase letters with some numbers generated randomly with some special kind of text type font. It is mainly used for Human Verification whether the user is human or any computer script. In this tutorial we will teach you how to make your own captcha system with the help of PHP and Ajax.