/// <summary>
        /// 获取验证码【字符串】
        /// </summary>
        /// <param name="Length">验证码长度【必须大于0】</param>
        /// <returns></returns>
        public static string VerficationText(int Length)
        {
            char[] _verfication=new char[Length];
            Random _random = new Random();
            char[] _dictionary = { 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9' };
            for (int i = 0; i < Length; i++)
            {
                _verfication[i] = _dictionary[_random.Next(_dictionary.Length - 1)];
            }
            return new string(_verfication);
        }

 /// <summary>
        /// 产生验证码方法
        /// </summary>
        /// <returns></returns>
        public void VerificationCode()
        {
            int _verificationLength = 6;
            int _width = 100, _height = 20;
            SizeF _verificationTextSize;
            string path = Server.MapPath("~/Skins/Commmon/Texture.jpg");//使用一张背景图
            Bitmap _bitmap = new Bitmap(path);
            TextureBrush _brush = new TextureBrush(_bitmap);
            //获取验证码
            string _verificationText = VerficationText(_verificationLength);
            //储存验证码
            Session["VerificationCode"] = _verificationText.ToUpper();
            Font _font = new Font("Arial", 14, FontStyle.Bold);
            Bitmap _image = new Bitmap(_width, _height);
            Graphics _g = Graphics.FromImage(_image);
            //清空背景色
            _g.Clear(Color.White);
            //绘制验证码
            _verificationTextSize = _g.MeasureString(_verificationText, _font);
            _g.DrawString(_verificationText, _font, _brush, (_width - _verificationTextSize.Width) / 2, (_height - _verificationTextSize.Height) / 2);
            _image.Save(Response.OutputStream, System.Drawing.Imaging.ImageFormat.Jpeg);
        }