生成验证码

private byte[] GetValidateCodeImage()
        {
            string VNum = RndNum(4);
            Bitmap Img = new Bitmap(VNum.Length * 16, 25);
            Graphics g = Graphics.FromImage(Img);
            g.DrawString(VNum, (new Font("Verdana", 10)), (new SolidBrush(Color.FromArgb(85,85,85))), 3, 3);
            MemoryStream ms = new MemoryStream();
            Img.Save(ms, ImageFormat.Png);
            g.Dispose();
            Img.Dispose();
            Session["LocalAuthCode"] = VNum;
            return ms.ToArray();
        }

        private string RndNum(int VcodeNum)
        {
            string str = @"0123456789abcdefghigklmnopqrstuvwxyzABCDEFGHIGKLMNOPQRSTUVWXYZ";
            string VNum = "";
            Random rnd = new Random();
            for (int i = 0; i < VcodeNum; i++)
            {
                VNum = VNum + str.Substring(0 + rnd.Next(61), 1);
            }
            return VNum;
        }