This tutorial teaches you how to create and add a simple but powerful Anti-Spam Captcha to your system or application using PHP.
A good way to avoid automatic form submissions when creating a web form or to prevent automated web robot tools and spammers from taking advantage of your forms and scripts is to use some kind of verification process.
One of the best ways is to use an image verification also known as Captcha. What it does is to dynamically create an image with a random string displayed on it. Then visitors or users of your website are asked to type that string in a text field and once the form is submitted, it checks if the string on the image matches the one inputted by the user.
Because there is no easy way to read a text from an image (image recognition) this is a good way to protect your web forms from spammers.
The system is very easy to understand and customize with good programming code comments to ease usability.