/// <summary>
        /// Asynchronous update of the new CAPTCHA.
        /// </summary>
        /// <param name="l">length</param>
        /// <returns></returns>
        public ActionResult NewCaptcha(int l)
        {
            if (l < 4)
            {
                l = 4;
            }
            if (Request.IsAjaxRequest())
            {
                var captcha = CaptchaHelper.GeneratePartialCaptcha(Request.RequestContext, l);
                return(JavaScript(string.Format(ReturnScript, captcha.Code, captcha.Image)));
            }

            return(Redirect(Request.UrlReferrer.AbsolutePath));
        }