带ASP.NET_SessionId获取验证码问题？
public Bitmap GetCodeImage()
  {
  string cookieHeader = "rtime=1; ltime=1321858632937; cnzz_eid=98605368-1321679713-; cnzz_a644725=10; sin644725=none; ASP.NET_SessionId=zoojtrmg0jjb1cfkj5unpj3n; rtime=0; ltime=1321703051546; cnzz_eid=24475558-1321703043-http%3A//cn.bing.com/search%3Fq%3Dwww.100mai.net%26src%3DIE-SearchBox%26FORM";
  HttpWebRequest httpWebRequest = (HttpWebRequest)HttpWebRequest.Create("http://www.100mai.net/admin/checkCode.aspx");
  CookieContainer co = new CookieContainer();
  co.SetCookies(new Uri("http://www.100mai.net"), cookieHeader);
  httpWebRequest.CookieContainer = co;

  httpWebRequest.Accept = "*/*";
  httpWebRequest.Referer = config.LoginUrl;
  httpWebRequest.UserAgent = " Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.2; Trident/4.0; .NET CLR 1.1.4322; .NET CLR 3.0.04506.648; .NET CLR 3.5.21022; .NET4.0C; .NET4.0E; .NET CLR 2.0.50727)";
  httpWebRequest.Method = "GET";
  httpWebRequest.Headers.Set("Accept-Encoding", "gzip, deflate");
  httpWebRequest.Headers.Set("Accept-Language", "zh-CN");
  httpWebRequest.KeepAlive = true;

  HttpWebResponse webResponse = (HttpWebResponse)httpWebRequest.GetResponse();
  Stream responseStream = webResponse.GetResponseStream();
  Image original = Image.FromStream(responseStream);
  Bitmap bitMap = new Bitmap(original);
  responseStream.Close();
  return bitMap;
  }
问题：为什么用同一个ASP.NET_SessionId每次获取的验证码不一样。
是按http://topic.csdn.net/u/20100604/18/fadb1e99-e010-4aad-9e4f-bf5f0f745ee1.html的方法改的。

------解决方案--------------------
http://www.haogongju.net/art/235438
------解决方案--------------------
验证码一次请求就重新生成的。你第一次get之后就别再刷了。
------解决方案--------------------
使用C#登录带验证码的网站
------解决方案--------------------

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http://www.haogongju.net/art/235438