I provide you with this easy-to-use Captcha generator.
As easy as ABC! Demo PHP scripts are provided as part of the package.
As this project is fully Open-Source,
you can use it however you want on your own website.
Download links :
Captchas text is kept server-side in a session variable,
thus remaining unavailable to hackers.
The script uses image caching with IP attribution
for better server performance
without compromizing security.
Size, color, complexity : the captchas are fully customizable.
Be careful though!
Keep in mind that there is no 100% reliable method
to distinguish bots from regular users.
The best way to control what happens on your website is to keep your eyes open.