asp.net后台模拟其他网站带验证码登陆

/// <summary>
/// 获取其他网站通行证
/// </summary>
/// <param name="postUrl">网站地址</param>
/// <param name="cookie">网站cookie</param>
/// <returns></returns>
public static  CookieContainer GetCookie(string postUrl,CookieContainer cookie) 
{

HttpWebRequest request;   
HttpWebResponse response;   
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())   
{ 
cookie.Add(response.Cookies);
}
}
catch{}
return cookie;
}
/// <summary>
/// 获取验证码位图