BotDetect ASP.NET CAPTCHA 2.0.12.0 offers you a professional security application. This software is designed to protect protect your registration, comment, poll, guestbook, content submission, and other online forms from automated spam submissions. It generates CAPTCHA images with textual code rendered in them that are easily decipherable to humans - but not to spam bots.
In essence, it allows you to focus on your code or content -- instead of on deleting spam.

Major features

1. time unlimited and fully functional demo version (it displays "Lanap" 50% of times),
2. built-in sound support that allows access even to visually impaired people,
3. 50 different CAPTCHA algorithms,
4. customizable image size and format,
5. SharePoint 2007 compatible,
6. ASP.NET Ajax compatible,
7. XHTML 1.1 Strict compliant markup,
8. full server side component,
9. works on shared servers (medium trust support)
10. not dependent on other software so it does not bring in any additional dependencies,
11. includes high-quality samples,
12. free 24x7 support.

Improvements of this version:

Added "Reload CAPTCHA" button support, ASP.NET Ajax built-in compatibility, built-in SharePoint support, rewrote the Captcha control rendering code to produce smaller, semantic, XHTML 1.1 Strict compliant markup

Requirements:

1. Windows,
2. IIS,
3. .NET 1.1 - 3.5