Step 1 Create the Empty ASP.NET MVC application.

Step 2 Add the CaptchaMvc library to the Reference Layer like this 

Step 3 In the Model layer add a User class and create the property like this.

    public class User
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public string LastName { get; set; }
    }

Step 4 Create a HomeController and write the action method like this.

using CaptchaMvc.HtmlHelpers;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Mvc;

namespace MVCCaptcha.Controllers
{
    public class HomeController : Controller
    {
        public ActionResult Index()
        {
            return View();
        }

        public ActionResult About()
        {
            ViewBag.Message = "Your application description page.";

            return View();
        }

        public ActionResult Contact()
        {
            ViewBag.Message = "Your contact page.";

            return View();
        }

        [HttpPost]
        public ActionResult Index(string empty)
        {
            // Code for validating the CAPTCHA  
            if (this.IsCaptchaValid("Captcha is not valid"))
            {

                return RedirectToAction("ThankYouPage");
            }

            ViewBag.ErrMessage = "Error: captcha is not valid.";
            return View();
        }

        public ActionResult ThankYouPage()
        {
            return View();
        }

    }
}

Note: Do not forget to use the CAPTCHA MVC.HtmlHelpers namespace. In the post action method I wrote code for CAPTCHA validation.

Step 5 Now create the Index View like this.

Right-click on Index view then click on Add View 

@using CaptchaMvc.HtmlHelpers
@using MVCCaptcha;
@using CaptchaMvc;

@model MVCCaptcha.Models.User

@{
    ViewBag.Title = "Index";
}

@using (Html.BeginForm())
{
    @Html.ValidationSummary(true)

    <fieldset>
        <legend>User Details</legend>

        <div class="editor-label">
            @Html.LabelFor(model => model.Name)
        </div>
        <div class="editor-field">
            @Html.EditorFor(model => model.Name)
            @Html.ValidationMessageFor(model => model.Name)
        </div>

        <div class="editor-label">
            @Html.LabelFor(model => model.LastName)
        </div>
        <div class="editor-field">
            @Html.EditorFor(model => model.LastName)
            @Html.ValidationMessageFor(model => model.LastName)
        </div>

        @Html.MathCaptcha()

        @*@Html.Captcha(3)*@
        <br />
        <p class="Error">  @ViewBag.ErrMessage </p>
        <p>
            <input type="submit" value="Send" />
        </p>
    </fieldset>
} 

Note: Here if you use the @Html.MathCaptcha() helper class then it will generate a mathmatical CAPTCHA. If you use the @Html. Captcha(3) helper class then it will generate a Char CAPTCHA. 3 is the length of the CAPTCHA.

Step 6: Create the ThankYouPage index like this.

Right-click on ThankYouPage view then click on Add View

@model MVCCaptcha.Models.User

@{
    ViewBag.Title = "ThankYouPage";
}

<h2>ThankYouPage</h2>

<b> Thank you for submitting your details.</b>  

Here we saw how to use a CAPTCHA in an ASP.NET MVC application. It is very simple and straight forward to implement in MVC applications.

Run the project to see the output