Alright, we've all seen it more and more around the 'net - those images that accompany a form, you know the ones. They have the "fuzzy" background and the letters/numbers over the top of it. Well, they're there to make sure that it's a real human filling out this form, and this new tutorial from Zend will show you how to make your own.

Every site administrator wants to be sure that a real person filled out the form on their site, not a 'script'. Especially if the form returns valuable information that others would like. [...] You can never completely protect your sources being grabbed, but you can set some traps that scripts can’t jump over. The most widely used trap is a noisy image, which a human’s eye can read easily but no algorhytm can.

They get into the details of how to use GD to create a dynamic image for your form. They give you the code to generate it, the image code to create it, and the validation routine to check it. These images can be amazingly effective, especially for forms that you want a bit more reassurance that it's a real person on the other end...