How to Create PHP Captcha

In Programming, captcha are used to check that weather you are human or a bot. These captcha images contains some readable text with some noise, shape, distortion, lines and dots, which are readable by human and who can write it into the captcha input field to confirm that user is human, not a bot.
There are ready made third party captcha plugins available on the internet such as ReCaptcha, aim of this tutorial is to share knowledge that how captcha works and how can we create our own custom captcha.
Requirement:
Please make sure that GD(Graphics Draw) library is installed on your host. Mostly web host already have it. But if you don’t then you can install it, follow instructions or ask you web hosting company to install it.
Steps to create a Captcha Using PHP
1. Create an index.php file
2. Create a captcha.php file