Php Captcha Script

We have generated and Anti-Spam code image in the Guest book sign up page and have done the validation for this code.

In the guest book sign up page, we have displayed an Anti-Spam code image which has an unique random alphanumeric characters. This code will change for each time. Once the user submits his/her sign up form, we have done the validation for this Anti-Spam code. The user can register to the guest book, only if the code is valid. The code is case-sensitive. So the user has to enter the exact character that they view. The background of the image will also vary with time.