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The Captcha Audio

To provide accessibility to visually impaired users, Captcha's distorted image can be represented in an audio format. Every alphanumeric character is read out using the NATO phonetic alphabet.

By default, an audio button that provides a voice-over for the respective image is rendered next to the Captcha. A slider that allows the user to adjust the volume of the audio is also provided.

Enabling Captcha Audio

The Kendo UI Captcha server-side provider creates an audio file based on the content of the image. To enable voice-over of the Captcha in your project:

  1. Add the Captcha server-side provider to your project.

  2. Add the AudioHandler option to your Captcha and send a request to the remote endpoint and include the Captcha's ID as an additional parameter.

            handler: "./reset",
            audioHandler: function (args) {
                args.success("./audio?captchaId=" +;
            validationHandler: "./validate",
            error: function (data) {
  3. Use the CaptchaHelper.SpeakText() method to create a wav File. Return it to the client-side.

    public ActionResult Audio(string captchaId)
        CaptchaImage captcha = (CaptchaImage)Session["captcha" + captchaId];
        byte[] bmpBytes;
        using (MemoryStream audio = CaptchaHelper.SpeakText(captcha))
            bmpBytes = audio.ToArray();
        return File(bmpBytes, "audio/wav");
  4. The Kendo UI Captcha starts the voice-over of the image after the user clicks the Audio button.

See Also

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