This plugin does not work alone and is intended to work with other plugins. It is originally created for Contact Form 7, however, you can use it with your own plugin.
This plugin does not use PHP “Sessions” for storing states, unlike many other PHP CAPTCHA solutions but stores them as temporary files. This allows you to embed it into WordPress without worrying about conflicts.
When you generate a CAPTCHA, it creates two files for it. One is an image file of CAPTCHA and the other is a PHP file which returns the correct answer to the CAPTCHA.
Requires WordPress Version: 2.8 or higher