Recently I started to get a lot of junk in my in-box through the contact form. This was all generated by spam bots on the net so I added in the new feature of human evaluation by use of the image with a number on the contact and comment forms to slow the junk entering my in-box. This technique is known as CAPTCHA (Completely Automated Public Turing to tell Computers from Humans Apart).
A CAPTCHA test is a program that can generate and grade tests that most humans can pass and current computer programs can’t pass.
The first part of this is to get a suitably random number and store it somewhere. I have used a session variable so that I can reuse the random function.
Generating the image using that number looks like this, I have saved this in a PHP file and we will look at how to call this in a minute. The code comments should be explanation enough on how it works.
Now because we put the random number in the user Session, it makes it really easy to get a hold of it on processing the form.