c# 获取网站验证码图片

/// <summary>
       /// 获取网页验证码
       /// </summary>
       /// <param name="server">服务器地址</param>
       /// <param name="URL">网页地址</param>
       /// <param name="byteRequest">字节数组，存放图片字节</param>
       /// <param name="cookie">网站分配给客户的临时sessionid（临时cookie值），并非真正cookie</param>
       /// <param name="header"></param>
       /// <returns>图片的二进制数组</returns>
        public static byte[] GetHtmlByBytes(string server, string URL, byte[] byteRequest, string cookie, out string header)
        {
            long contentLength;
            HttpWebRequest httpWebRequest;
            HttpWebResponse webResponse;
            Stream getStream;

            httpWebRequest = (HttpWebRequest)HttpWebRequest.Create(URL);
            CookieContainer co = new CookieContainer();
            co.SetCookies(new Uri(server), cookie);  
            httpWebRequest.CookieContainer = co;
            httpWebRequest.ContentType = "application/x-www-form-urlencoded";
            httpWebRequest.Method = "Post";
            httpWebRequest.ContentLength = byteRequest.Length;
            Stream stream;
            stream = httpWebRequest.GetRequestStream();
            stream.Write(byteRequest, 0, byteRequest.Length);
            stream.Close();
            webResponse = (HttpWebResponse)httpWebRequest.GetResponse();
            header = webResponse.Headers.ToString();
            getStream = webResponse.GetResponseStream();
            contentLength = webResponse.ContentLength;

            byte[] outBytes = new byte[contentLength];
            outBytes = ReadFully(getStream);
            getStream.Close();
            return outBytes;
        }