Notes

using System;
using System.Drawing;
using System.Drawing.Imaging;
using System.IO;
using System.Web.Mvc;

namespace YourNamespace.Controllers
{
public class CaptchaController : Controller
{
private const string CaptchaSessionKey = "CaptchaCode";

public ActionResult Index()
{
// Generate a new CAPTCHA code
string captchaCode = GenerateCaptchaCode();

// Save the CAPTCHA code in session
Session[CaptchaSessionKey] = captchaCode;

// Generate the CAPTCHA image
byte[] captchaImage = GenerateCaptchaImage(captchaCode);

// Return the CAPTCHA image as a FileResult
return File(captchaImage, "image/png");
}

[HttpPost]
public ActionResult Validate(string userInput)
{
// Retrieve the CAPTCHA code from session
string captchaCode = Session[CaptchaSessionKey] as string;

// Check if the user input matches the CAPTCHA code
bool isValid = userInput.Equals(captchaCode, StringComparison.OrdinalIgnoreCase);

// You can use the isValid flag to perform further actions, like redirecting or showing a message

return Content(isValid ? "Valid CAPTCHA" : "Invalid CAPTCHA");
}

private string GenerateCaptchaCode()
{
// Generate a random CAPTCHA code (you can customize this method further if needed)
Random random = new Random();
const string chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
return new string(Enumerable.Repeat(chars, 6).Select(s => s[random.Next(s.Length)]).ToArray());
}

private byte[] GenerateCaptchaImage(string captchaCode)
{
// Generate the CAPTCHA image (you can customize the appearance and font)
using (Bitmap bitmap = new Bitmap(200, 50))
{
using (Graphics graphics = Graphics.FromImage(bitmap))
{
graphics.Clear(Color.White);
Font font = new Font("Arial", 20, FontStyle.Bold);
PointF point = new PointF(10f, 10f);
graphics.DrawString(captchaCode, font, Brushes.Black, point);
}

// Convert the bitmap to a byte array
using (MemoryStream stream = new MemoryStream())
{
bitmap.Save(stream, ImageFormat.Png);
return stream.ToArray();
}
}
}
}
}

@{
ViewBag.Title = "CAPTCHA Validation";
}

<h2>CAPTCHA Validation</h2>

@using (Html.BeginForm("Validate", "Captcha", FormMethod.Post))
{
<div>
<img src="@Url.Action("Index", "Captcha")" alt="CAPTCHA Image" />
<br />
<label for="captchaInput">Enter the CAPTCHA code:</label>
<input type="text" id="captchaInput" name="userInput" />
<br />
<input type="submit" value="Submit" />
<a href="@Url.Action("Index", "Captcha")">Refresh CAPTCHA</a>
</div>
}
<system.web>
<sessionState mode="InProc" />
<!-- Other configurations -->
</system.web>