You may be thinking just exactly what is a captcha? Well you are likely to have already seen them across the web. They are those little images with a code on the front that you type into a box in order to submit something. This kind of system helps to prevent automatic submitting of an operation by some kind of program or robot. In this tutorial I will show you how to make a CAPTCHA just like the one below. Its not the most advanced captcha available because it uses a simple system font and nothing more.
The lines that you see above are to make any robots job of trying to work out that code a little harder. The dots in the background also help with this. Follow the link to learn more about how to create CAPTCHA.