//获取验证码
        public string GetVerifyCode(string sourceUrl)//获取验证码
        {
            CookieContainer cc = new CookieContainer();
            HttpWebRequest req = (HttpWebRequest)HttpWebRequest.Create(sourceUrl);
            req.CookieContainer = cc;
            using (WebResponse res = req.GetResponse())
            {
                System.Drawing.Image bmp = Bitmap.FromStream(res.GetResponseStream());
                bmp.Save("c:/1.jpg", ImageFormat.Jpeg);
                return null;
            }
        }

上面是核心代码。获取验证码图片后，放置在C盘，命名为1.jpg。