Codewalkers.com has a new tutorial posted today showing the creation of a CAPTCHA image with PHP.
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.
They start with a look at how CAPTCHAs work before even looking at the code. The next steps include the creation of the random string of characters and placing them in the image (with a standard background in this case). The image is built with the GD functionality in PHP. Finally, they add the functionality in, checking a session variable, to ensure that the user has inputted the text from the image correctly.