.net怎么使用WebRequest获取远程服务器的图片

/// 

        /// 获取网页验证码图片
        /// 

        /// 
        /// 
        /// 
        public static Stream GetWebImage(string url, CookieContainer cookie)
        {
            HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);
            request.Referer = referer;
            request.UserAgent = "Mozilla/5.0 (Windows NT 5.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/31.0.1650.63 Safari/537.36";
            request.Accept = "image/webp,*/*;q=0.8";
            request.CookieContainer = cookie;
            request.ContentType = contentType;
            request.KeepAlive = true;
            request.UseDefaultCredentials = true;
            //  request.Proxy = null;
            return request.GetResponse().GetResponseStream();
        }

Stream stream = GetWebImage(url, cookieContainer);
            Image image = Image.FromStream(stream);
            pictureBox1.Image = image;