Webcontrolcaptcha image not showing

With IIS7 integrated mode, make sure you add the handler in the right section

<configuration>
  <system.webServer>
    <handlers>
      <add name="CaptchaImage"
        verb="*"
        path="CaptchaImage.aspx"
        preCondition="integratedMode"
        type="WebControlCaptcha.CaptchaImageHandler, WebControlCaptcha"/>
    </handlers>
  </system.webServer>
</configuration>