MS Captcha not working with IIS

////////////////////
Step 1. Create Application pool for project and set -

Managed Pipeline Mode - Classic

Step 2. Set Handler in web.config file inside the system.web -

<system.web>   

    <httpHandlers>

      <add verb="GET" path="CaptchaImage.axd" type="MSCaptcha.CaptchaImageHandler, MSCaptcha"/>

</system.web>    

Step 3. Set allow for the users inside the location tag 

<location path="CaptchaImage.axd">

    <system.web>

      <authorization>

        <allow users="*" />

      </authorization>

    </system.web>

  </location>