c# 获取页面的登入的验证码

我是新手想做一个登入
我老获取不到验证码
高手帮帮忙啊！！！using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Net;
using System.Collections;
using System.IO;namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        CookieContainer cookie = new CookieContainer();
        public Form1()
        {
            InitializeComponent();
        }        private void Form1_Load(object sender, EventArgs e)
        {
            GetHtmlData("http://www.doubao.com/user/login", cookie);
            DowloadCheckImg("http://www.doubao.com/auth/checkcode/",cookie,@"C:\111.png");        } 
        /// <summary>  
        /// 通过get方式请求页面，传递一个实例化的cookieContainer  
        /// </summary>  
        /// <param name="postUrl"></param>  
        /// <param name="cookie"></param>  
        /// <returns></returns>  
        public static ArrayList GetHtmlData(string postUrl, CookieContainer cookie)
        {
            HttpWebRequest request;
            HttpWebResponse response;
            ArrayList list = new ArrayList();
            request = WebRequest.Create(postUrl) as HttpWebRequest;
            request.Method = "GET";
            request.UserAgent = "Mozilla/4.0";
            request.CookieContainer = cookie;
            request.KeepAlive = true;            request.CookieContainer = cookie;
            try
            {
                //获取服务器返回的资源  
                using (response = (HttpWebResponse)request.GetResponse())
                {
                    using (StreamReader reader = new StreamReader(response.GetResponseStream(), Encoding.Default))
                    {
                        cookie.Add(response.Cookies);
                        //保存Cookies  
                        list.Add(cookie);
                        list.Add(reader.ReadToEnd());
                        list.Add(Guid.NewGuid().ToString());//图片名  
                    }
                }
            }
            catch (WebException ex)
            {
                list.Clear();
                list.Add("发生异常/n/r");
                WebResponse wr = ex.Response;
                using (Stream st = wr.GetResponseStream())
                {
                    using (StreamReader sr = new StreamReader(st, System.Text.Encoding.Default))
                    {
                        list.Add(sr.ReadToEnd());
                    }
                }
            }
            catch (Exception ex)
            {
                list.Clear();
                list.Add("5");
                list.Add("发生异常：" + ex.Message);
            }
            return list;
        }
        /// <summary>  
        /// 下载验证码图片并保存到本地  
        /// </summary>  
        /// <param name="Url">验证码URL</param>  
        /// <param name="cookCon">Cookies值</param>  
        /// <param name="savePath">保存位置/文件名</param>  
        public static bool DowloadCheckImg(string Url, CookieContainer cookCon, string savePath)
        {
            bool bol = true;
            HttpWebRequest webRequest = (HttpWebRequest)WebRequest.Create(Url);
            //属性配置  
            webRequest.AllowWriteStreamBuffering = true;
            webRequest.Credentials = System.Net.CredentialCache.DefaultCredentials;
            webRequest.MaximumResponseHeadersLength = -1;
            webRequest.Accept = "image/gif, image/x-xbitmap, image/jpeg, image/pjpeg, application/x-silverlight, application/x-ms-application, application/x-ms-xbap, application/vnd.ms-xpsdocument, application/xaml+xml, application/vnd.ms-excel, application/vnd.ms-powerpoint, application/msword, application/QVOD, application/QVOD, */*";
            webRequest.UserAgent = "Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1; (R1 1.5); .NET CLR 2.0.50727; .NET CLR 3.0.04506.648; .NET CLR 3.5.21022; InfoPath.2; .NET4.0C; .NET4.0E; Alexa Toolbar; u9dnfsh)";
            webRequest.ContentType = "application/x-www-form-urlencoded";
            webRequest.Method = "GET";
            webRequest.Headers.Add("Accept-Language", "zh-cn");
            webRequest.Headers.Add("Accept-Encoding", "gzip,deflate");
            webRequest.KeepAlive = true;
            webRequest.CookieContainer = cookCon;
            try
            {
                //获取服务器返回的资源  
                using (HttpWebResponse webResponse = (HttpWebResponse)webRequest.GetResponse())
                {
                    using (Stream sream = webResponse.GetResponseStream())
                    {
                        List<byte> list = new List<byte>();
                        while (true)
                        {
                            int data = sream.ReadByte();
                            if (data == -1)
                                break;
                            list.Add((byte)data);
                        }
                        File.WriteAllBytes(savePath, list.ToArray());
                    }
                }
            }
            catch (WebException ex)
            {
                bol = false;
            }
            catch (Exception ex)
            {
                bol = false;
            }
            return bol;
        }        
    }
}