simple Captcha in MVC

Simple Captcha In MVC :

In Model:

 public class SubscribeModel

    {

        //model specific fields

        [Required]

        [Display(Name = "How much is the sum")]

        public string Captcha { get; set; }

    }

In Controller:

Name Spaces in controller:

using System.Drawing;

using System.IO;

using System.Drawing.Drawing2D;

using System.Drawing.Text;

using JQGridExample.Models;

public ActionResult Index()

   {

            return View();

   }

   public ActionResult CaptchaImage(string prefix, bool noisy = true)

        {

            var rand = new Random((int)DateTime.Now.Ticks);

            //generate new question

            int a = rand.Next(10, 99);

            int b = rand.Next(0, 9);

            var captcha = string.Format("{0} + {1} = ?", a, b);

            //store answer

            Session["Captcha" + prefix] = a + b;

            //image stream

            FileContentResult img = null;

            using (var mem = new MemoryStream())

            using (var bmp = new Bitmap(130, 30))

            using (var gfx = Graphics.FromImage((Image)bmp))

            {

                gfx.TextRenderingHint = TextRenderingHint.ClearTypeGridFit;

                gfx.SmoothingMode = SmoothingMode.AntiAlias;

                gfx.FillRectangle(Brushes.White, new Rectangle(0, 0, bmp.Width, bmp.Height));

                //add noise

                if (noisy)

                {

                    int i, r, x, y;

                    var pen = new Pen(Color.Yellow);

                    for (i = 1; i < 10; i++)

                    {

                        pen.Color = Color.FromArgb(

                        (rand.Next(0, 255)),

                        (rand.Next(0, 255)),

                        (rand.Next(0, 255)));

                        r = rand.Next(0, (130 / 3));

                        x = rand.Next(0, 130);

                        y = rand.Next(0, 30);

                        gfx.DrawEllipse(pen,x-r, y-r,r,r);

                    }

                }

                //add question

                gfx.DrawString(captcha, new Font("Tahoma", 15), Brushes.Gray, 2, 3);

                //render as Jpeg

                bmp.Save(mem, System.Drawing.Imaging.ImageFormat.Jpeg);

                img = this.File(mem.GetBuffer(), "image/Jpeg");

            }

            return img;

        }

        [HttpPost]

        public ActionResult Index(SubscribeModel model)

        {

            //validate captcha

            if (Session["Captcha"] == null || Session["Captcha"].ToString() != model.Captcha)

            {

                ModelState.AddModelError("Captcha", "Wrong value of sum, please try again.");

                //dispay error and generate a new captcha

                return View(model);

            }

            return View("ThankYouPage");

        }

        public ActionResult ThankYouPage()

        {

            return View();

        }

In View:

@model JQGridExample.Models.SubscribeModel

@{

    ViewBag.Title = "CaptchaImage";

}

<h2>CaptchaImage</h2>

@using(Html.BeginForm()){

    <table>

        <tr>

            <td> @Html.LabelFor(model => model.Captcha)

    <a href="@Url.Action("Index","Add")">

        <img alt="Captcha" src="@Url.Action("CaptchaImage")" style="" />

    </a> </td>

            <td> @Html.TextBoxFor(model => model.Captcha)

    @Html.ValidationMessageFor(model => model.Captcha) </td>

        </tr>

        <tr><td><input type="submit" value="submit" /></td</tr>

    </table>

}