下面 是获取验证码图片的方法

 public static CookieContainer cookies = new CookieContainer();

public static string doGetImg(string Url)
{
try
{
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(Url.ToString());
request.Headers.Add(HttpRequestHeader.AcceptEncoding, "gzip,deflate");
request.Headers.Add(HttpRequestHeader.AcceptLanguage, "zh-CN");
request.Accept = "text/html, application/xhtml+xml,*/*";
request.KeepAlive = true;

request.UserAgent = "User-Agent Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; WOW64; Trident/5.0)";
request.Method = "get";
request.ContentType = "application/x-www-form-urlencoded";
request.AllowAutoRedirect = true;
request.Credentials = CredentialCache.DefaultCredentials;
request.Host = "www.luck.net";
request.CookieContainer = new CookieContainer(); //暂存到新实例
HttpWebResponse response = (HttpWebResponse)request.GetResponse();


string kes = response.ContentEncoding.ToLower();
Stream responseStream = null;
MemoryStream ms = null;
if (response.ContentEncoding.ToLower() == "gzip")
{
responseStream = new GZipStream(response.GetResponseStream(), CompressionMode.Decompress);
using (var stream = responseStream)
{
Byte[] buffer = new Byte[4096];
int offset = 0, actuallyRead = 0;
do
{
actuallyRead = stream.Read(buffer, offset, buffer.Length - offset);
offset += actuallyRead;
}
while (actuallyRead > 0);
ms = new MemoryStream(buffer);
}

}
cookies = request.CookieContainer; //保存cookies
response.Close();
// cookiesstr = request.CookieContainer.GetCookieHeader(request.RequestUri); //把cookies转换成字符串
System.Drawing.Image img = Bitmap.FromStream(ms);
string fn = System.IO.Path.Combine("/Resource/UploadFile/", Guid.NewGuid().ToString() + ".jpg");
string address = HttpContext.Current.Server.MapPath(fn);
img.Save(address, ImageFormat.Jpeg);
return fn;
}
catch
{
return null;
}
}

这个是模拟提交的方法

public static void PostLogin(string loginUrl, string account, string password, string code)
{
HttpWebRequest request = null;
HttpWebResponse response = null;
try
{
string postdata = "kcUserName=" + account + "&kc_j_captcha_response=" + code.ToLower() + "&kcPassword=" + password;//模拟请求数据，数据样式可以用FireBug插件得到。
request = (HttpWebRequest)WebRequest.Create(loginUrl);//实例化web访问类
request.Headers.Add(HttpRequestHeader.AcceptEncoding, "gzip,deflate");
request.Headers.Add(HttpRequestHeader.AcceptLanguage, "zh-CN");
request.Accept = "text/html, application/xhtml+xml,*/*";
request.KeepAlive = true;
request.Referer = "http://www.luck.net/kcLogin.action";
request.Headers.Add(HttpRequestHeader.CacheControl, "no-cache");
request.UserAgent = "User-Agent Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; WOW64; Trident/5.0";
request.Method = "POST";
request.ContentType = "application/x-www-form-urlencoded";
request.AllowAutoRedirect = true;
request.Credentials = CredentialCache.DefaultCredentials;

request.Host = "www.luck.net";
// request.AllowAutoRedirect = false; // 不用需自动跳转
//必须设置CookieContainer存储请求返回的Cookies
if (cookies != null)
{
request.CookieContainer = cookies;
}
else
{
request.CookieContainer = new CookieContainer();
cookies = request.CookieContainer;
}
//提交请求
byte[] postdatabytes = Encoding.UTF8.GetBytes(postdata);
request.ContentLength = postdatabytes.Length;
Stream stream;
stream = request.GetRequestStream();
//设置POST 数据
stream.Write(postdatabytes, 0, postdatabytes.Length);
stream.Close();
//接收响应
response = (HttpWebResponse)request.GetResponse();
string sdp = response.ContentEncoding.ToLower();
//保存返回cookie
// bCookie.upcookie(response.Cookies);
response.Cookies =request.CookieContainer.GetCookies(request.RequestUri);
CookieCollection cook = response.Cookies;
string strcrook = request.CookieContainer.GetCookieHeader(request.RequestUri);
CookiesString = strcrook;
Stream responseStream = null;
if (response.ContentEncoding.ToLower() == "gzip")
{
responseStream = new System.IO.Compression.GZipStream(response.GetResponseStream(), System.IO.Compression.CompressionMode.Decompress);
}
else if (response.ContentEncoding.ToLower() == "deflate")
{
responseStream = new System.IO.Compression.DeflateStream(response.GetResponseStream(), System.IO.Compression.CompressionMode.Decompress);
}
else
{
responseStream = response.GetResponseStream();
}
StreamReader sr = new StreamReader(responseStream, Encoding.UTF8);
string content = sr.ReadToEnd();
sr.Close();
request.Abort();
response.Close();
if (content.Contains("验证码错误"))
{
ShowMsgHelper.Alert_Error("验证码错误");
return;
}

}
catch (Exception ex)
{

}
}

这个是登录网站http://www.luckyair.net/kcLogin.action