Disable Automated Signup...

Hi *!
I have for my website a form to sign-up for some service. Now, in order to disable automated sign-up I want to display some image (that displays some text) and the user types-in that text manually to be able to sign-up successfully. I am not sure what it is called :(, tried googling for "disable sign-up image" and some variants of it, but the results were not too much of help.

I am using php5 on my website.

Any comments/suggestions are highly appreciated,

Thanks in Advance,
Regards,
Usman.

PHP Image Verification is the term for which you are looking.

What you search is a CAPTCHA ("Completely Automated Public Turing test to tell Computers and Humans Apart")
http://en.wikipedia.org/wiki/CAPTCHA

Here are some examples on how to realize a captcha with php
http://www.white-hat-web-design.co.u...hp-captcha.php
http://www.codewalkers.com/c/a/Misce...TCHA-with-PHP/
http://www.phpriot.com/d/articles/ph...m-2/page3.html
http://captcha.megaleecher.net/

Thanks PeejAvery, Blueday both of you for your help. Appreciated!

Regards,
Usman.