Image does not display for Telerik RadCaptcha control

[Zaki]

I have a Telerik RadCaptcha control on my login page. However, despite all the settings and references included, the image does not display. It is working alright though, it is validating the captcha. The only problem is that since the image does not display, there is no way anybody can get it right.  Have attached a snapshot too.

[Vessy]

Hi Zaki,

When you are using authentication you should allow access to the RadCaptcha httpHandler to all users as shown in the following code snippet:

<location path="Telerik.Web.UI.WebResource.axd">
    <system.web>
        <authorization>
            <allow users="*"/>
        </authorization>
    </system.web>
</location>

Another possible cause for the problem can be if you are deploying you application into a load balanced environment, but the Captcha's image is stored in the application's cache instead of the session. You can refer the following help article for more details on how to configure RadCaptcha to work properly in such scenario:
http://docs.telerik.com/devtools/aspnet-ajax/controls/captcha/troubleshooting/using-webfarm-or-webgarden-environment

Regards,
Vessy
Telerik