Asp.net mvc 3 confirm code

    <script type="text/javascript">
        $(document).ready(function () {
            $("#validimg").click(function () {
                $("#validimg").attr('src', '@Url.Content("~/Home/GenerateImage?")' + Math.random());
            });
        })

    </script>

    <div>
        <img alt="验证码" id="validimg" src="@Url.Action("GenerateImage", "Home")" />
    </div>

    public class HomeController : Controller
    {

        public byte[] Test()
        {
            Random r = new Random((int)DateTime.Now.Ticks);
            int startChar = 64;
            string result = String.Empty;

            for (int i = 0; i < 4; i++)
            {
                int t = r.Next(1, 27);
                result += Convert.ToChar(t + startChar);
            }

            var image = new Bitmap((int)Math.Ceiling(result.Length * 15.0), 22);
            var g = Graphics.FromImage(image);
            try
            {
                var random = new Random();
                g.Clear(Color.White);

                for (int i = 0; i < 25; i++)
                {
                    var x1 = random.Next(image.Width);
                    var x2 = random.Next(image.Width);
                    var y1 = random.Next(image.Height);
                    var y2 = random.Next(image.Height);
                    g.DrawLine(new Pen(Color.Silver), x1, y1, x2, y2);
                }
                Font font = new Font("Arial", 12, (FontStyle.Bold | FontStyle.Italic));
                var brush = new LinearGradientBrush(new Rectangle(0, 0, image.Width, image.Height),
                Color.Blue, Color.DarkRed, 1.2f, true);
                g.DrawString(result, font, brush, 3, 2);
                //画图片的前景干扰点
                for (var i = 0; i < 100; i++)
                {
                    var x = random.Next(image.Width);
                    var y = random.Next(image.Height);
                    image.SetPixel(x, y, Color.FromArgb(random.Next()));
                }
                //画图片的边框线
                g.DrawRectangle(new Pen(Color.Silver), 0, 0, image.Width - 1, image.Height - 1);
                //保存图片数据
                var stream = new MemoryStream();
                image.Save(stream, ImageFormat.Jpeg);
                //输出图片流
                return stream.ToArray();
            }
            finally
            {
                g.Dispose();
                image.Dispose();
            }
        }

        //
        // GET: /Home/
        public ActionResult Index()
        {
            return View();
        }

        public ActionResult GenerateImage()
        {
            return File(Test(), @"image/gif");
        }
    }