//編碼例子
            System.IO.FileStream fs = System.IO.File.OpenRead("c://1.jpg");
            byte[] dt = new byte[fs.Length];
            fs.Read(dt, 0, (int)fs.Length);
            fs.Close();
            string s = Convert.ToBase64String(dt);
            fs = System.IO.File.OpenWrite("c://1.b64");
            dt = Encoding.Default.GetBytes(s);
            fs.Write(dt, 0, dt.Length);
            fs.Flush();
            fs.Close();
            //解碼例子
            System.IO.FileStream fs = System.IO.File.OpenRead("c://1.b64");
            byte[] dt = new byte[fs.Length];
            fs.Read(dt, 0, (int)fs.Length);
            string s = Encoding.Default.GetString(dt);
            dt = Convert.FromBase64String(s);
            fs = System.IO.File.OpenWrite("c://2.jpg");
            fs.Write(dt, 0, dt.Length);
            fs.Close();