Captcha Overview

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The Captcha is part of Telerik UI for ASP.NET MVC, a professional grade UI library with 110+ components for building modern and feature-rich applications. To try it out sign up for a free 30-day trial.

The Telerik UI Captcha HtmlHelper for ASP.NET MVC is a server-side wrapper for the Kendo UI DataSource widget.

The Telerik UI Captcha for ASP.NET MVC is a security measure that prevents automated spam from performing tasks such as form submissions in your ASP.NET MVC application. The widget generates distorted images of letters and numbers that are easily decipherable to humans, but not to automated programs (spam bots).

Basic Configuration

The following example demonstrates the basic configuration of the Captcha component. For the full server-side implementation, consider the Validation article.

    @(Html.Kendo().Captcha()
        .Name("Captcha")
        .Handler(handler => handler.Action("Reset", "Captcha")) // endpoint to return the CAPTCHA 
        .AudioHandlerFunction("audioHandler") // handler to fetch audio representation of the CAPTCHA (if needed)
        .ValidationHandler(handler => handler.Action("Validate", "Captcha")) // enpoint to validate the CAPTCHA
    )
    <script>
        function audioHandler(args) {
            args.success("@Url.Action("Audio")?captchaId=" + args.data.captchaId); 
        }
    </script>
public ActionResult Reset()
{
    CaptchaImage newCaptcha = SetCaptchaImage();

    return Json(new CaptchaModel
    {
        Captcha = "./shared/UserFiles/captcha/" + newCaptcha.UniqueId + ".png",
        CaptchaID = newCaptcha.UniqueId
    });
}

public ActionResult Validate(CaptchaModel model)
{
    string text = GetCaptchaText(model.CaptchaID);

    return Json(text ==  model.Captcha.ToUpperInvariant());
}

private string GetCaptchaText(string captchaId)
{
    string text = HttpContext.Session.GetString("captcha_" + captchaId);

    return text;
}

Functionality and Features

Events

For a complete example on the Captcha's events, refer to the demo on using the events of the Captcha.

Referencing Existing Instances

To reference an existing Captcha instance, use the jQuery.data() configuration option. Once a reference is established, use the Captcha client-side API to control its behavior.

    // Place the following after your Telerik UI Captcha for ASP.NET MVC declaration.
    <script>
        $(document).ready(function() {
            // The Name() of the Captcha is used to get its client-side instance.
            var captcha = $("#Captcha").data("kendoCaptcha");
        });
    </script>

See Also

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