Need a good captcha generating php script

Hello,

I need a good captcha generating php script. I searched on Google but din't found anything useful so far, I am interested in your personal suggestions, some php script that is easy to install and generates strong captchas.
:)

Not real familiar with what a "captcha" is. Please explain?

Captcha is a program generated image which contains alphanumeric code, which a user has to type while he posts in a forum, or while filling a form online.

captcha prevents spamming by program bots.

Do check http://www.hotscripts.com

U will get it..

I've checked that website but didn't find it..