在ASP.NET中创建CAPTCHA代码的代码？

using System;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Drawing.Imaging;
using System.IO;
using System.Web;

public class CaptchaImage : System.Web.UI.WebControls.Image
{
    private string _captchaText;

    public string CaptchaText
    {
        get { return _captchaText; }
    }

    protected override void OnLoad(EventArgs e)
    {
        base.OnLoad(e);

        // Generate a random captcha text
        _captchaText = GenerateRandomCaptchaText();

        // Create an image with the captcha text
        using (Bitmap bitmap = new Bitmap(120, 40, PixelFormat.Format24bppRgb))
        using (Graphics graphics = Graphics.FromImage(bitmap))
        {
            graphics.SmoothingMode = SmoothingMode.AntiAlias;
            graphics.FillRectangle(Brushes.White, 0, 0, bitmap.Width, bitmap.Height);
            using (Font font = new Font("Arial", 16, FontStyle.Bold))
            {
                graphics.DrawString(_captchaText, font, Brushes.Black, 10, 10);
            }

            // Add some random noise to the image
            for (int i = 0; i < 10; i++)
            {
                int x1 = new Random().Next(bitmap.Width);
                int y1 = new Random().Next(bitmap.Height);
                int x2 = new Random().Next(bitmap.Width);
                int y2 = new Random().Next(bitmap.Height);
                graphics.DrawLine(new Pen(Color.Black, 2), x1, y1, x2, y2);
            }

            // Save the image to a memory stream and set it as the image source
            using (MemoryStream memoryStream = new MemoryStream())
            {
                bitmap.Save(memoryStream, ImageFormat.Png);
                memoryStream.Seek(0, SeekOrigin.Begin);
                ImageUrl = "data:image/png;base64," + Convert.ToBase64String(memoryStream.ToArray());
            }
        }
    }

    private string GenerateRandomCaptchaText()
    {
        const string chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
        var random = new Random();
        var result = new string(
            Enumerable.Repeat(chars, 6)
                      .Select(s => s[random.Next(s.Length)])
                      .ToArray());
        return result;
    }
}

<uc1:CaptchaImage ID="CaptchaImage1" runat="server" />

if (CaptchaImage1.CaptchaText == userEnteredCaptchaText)
{
    // The CAPTCHA is valid
}
else
{
    // The CAPTCHA is invalid
}