C#(CAPTCHA for dotnet framework)

Installation instruction:

1. Unzip the downloaded file.
2. Copy MSCaptcha.dll and MSCaptcha.xml files to your /bin application directory.
3. In your ASP.NET application, add reference to mscaptcha.dll file.
4. Modify your web.config file, by adding this line to <httphandlers> section:
   <add verb="GET" path="CaptchaImage.axd" type="MSCaptcha.CaptchaImageHandler, MSCaptcha"/>
   
   If using IIS 7, add name parameter .
   If using Captcha version 4, use "MSCaptcha.captchaImageHandler" instead.
5. Add MSCaptcha control to your Visual Studio toolbox (optional)
6. That's it!

Example of use:

1. Add line to your .aspx file:
   <%@ Register Assembly="MSCaptcha" Namespace="MSCaptcha" TagPrefix="cc1" %>
2. Where needed, add the control itself:
   <cc1:CaptchaControl ID="ccJoin" runat="server" CaptchaBackgroundNoise="none" CaptchaLength="5"CaptchaHeight="60" CaptchaWidth="200" CaptchaLineNoise="None" CaptchaMinTimeout="5"CaptchaMaxTimeout="240" />
3. Put a textbox somewhere in your page where your user must enter what he sees in your captcha. Put this code (this example is in C#) to validate user input:
   
   ccJoin.ValidateCaptcha(txtCap.Text);if (!ccJoin.UserValidated)
   {
     //Inform user that his input was wrong ...  return;
   }
   
   In this particular example the ccJoin is the name of the Captcha control, the txtCap is the textbox where user entered what he sees in Captcha.

Captcha 2.0+ Download: Here... 

Captcha 4.0 Download: Here...