Create fancy CAPTCHA in ASP.net with Handler

 Create an handler "CaptchaHandler.ashx"

<%@ WebHandler Language="C#" Class="CaptchaHandler" %>

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

public class CaptchaHandler : IHttpHandler, IReadOnlySessionState
{
    public void ProcessRequest(HttpContext context)
    {
        SetCaptchaText(context);    // to get the random generate strings

        int iHeight = 80;
        int iWidth = 190;
        Random oRandom = new Random();

        int[] aBackgroundNoiseColor = new int[] { 150, 150, 150 };
        int[] aTextColor = new int[] { 0, 0, 0 };
        int[] aFontEmSizes = new int[] { 15, 20, 25, 30, 35 };

        string[] aFontNames = new string[]
{
 "Comic Sans MS",
 "Arial",
 "Times New Roman",
 "Georgia",
 "Verdana",
 "Geneva"
};
        FontStyle[] aFontStyles = new FontStyle[]
{ 
 FontStyle.Bold,
 FontStyle.Italic,
 FontStyle.Regular,
 FontStyle.Strikeout,
 FontStyle.Underline
};
        HatchStyle[] aHatchStyles = new HatchStyle[]
{
 HatchStyle.BackwardDiagonal, HatchStyle.Cross,
    HatchStyle.DashedDownwardDiagonal, HatchStyle.DashedHorizontal,
 HatchStyle.DashedUpwardDiagonal, HatchStyle.DashedVertical,
    HatchStyle.DiagonalBrick, HatchStyle.DiagonalCross,
 HatchStyle.Divot, HatchStyle.DottedDiamond, HatchStyle.DottedGrid,
    HatchStyle.ForwardDiagonal, HatchStyle.Horizontal,
 HatchStyle.HorizontalBrick, HatchStyle.LargeCheckerBoard,
    HatchStyle.LargeConfetti, HatchStyle.LargeGrid,
 HatchStyle.LightDownwardDiagonal, HatchStyle.LightHorizontal,
    HatchStyle.LightUpwardDiagonal, HatchStyle.LightVertical,
 HatchStyle.Max, HatchStyle.Min, HatchStyle.NarrowHorizontal,
    HatchStyle.NarrowVertical, HatchStyle.OutlinedDiamond,
 HatchStyle.Plaid, HatchStyle.Shingle, HatchStyle.SmallCheckerBoard,
    HatchStyle.SmallConfetti, HatchStyle.SmallGrid,
 HatchStyle.SolidDiamond, HatchStyle.Sphere, HatchStyle.Trellis,
    HatchStyle.Vertical, HatchStyle.Wave, HatchStyle.Weave,
 HatchStyle.WideDownwardDiagonal, HatchStyle.WideUpwardDiagonal, HatchStyle.ZigZag
};

        //Get Captcha in Session
        string sCaptchaText = context.Session["x"].ToString();

        //Creates an output Bitmap
        Bitmap oOutputBitmap = new Bitmap(iWidth, iHeight, PixelFormat.Format24bppRgb);
        Graphics oGraphics = Graphics.FromImage(oOutputBitmap);
        oGraphics.TextRenderingHint = TextRenderingHint.AntiAlias;

        //Create a Drawing area
        RectangleF oRectangleF = new RectangleF(0, 0, iWidth, iHeight);
        Brush oBrush = default(Brush);

        //Draw background (Lighter colors RGB 100 to 255)

        oBrush = new HatchBrush(aHatchStyles[oRandom.Next
            (aHatchStyles.Length - 1)], Color.FromArgb((oRandom.Next(100, 255)),
            (oRandom.Next(100, 255)), (oRandom.Next(100, 255))), Color.White);
        oGraphics.FillRectangle(oBrush, oRectangleF);

        System.Drawing.Drawing2D.Matrix oMatrix = new System.Drawing.Drawing2D.Matrix();
        int i = 0;
        for (i = 0; i <= sCaptchaText.Length - 1; i++)
        {
            oMatrix.Reset();
            int iChars = sCaptchaText.Length;
            int x = iWidth / (iChars + 1) * i;
            int y = iHeight / 2;

            //Rotate text Random
            oMatrix.RotateAt(oRandom.Next(-40, 40), new PointF(x, y));
            oGraphics.Transform = oMatrix;

            //Draw the letters with Random Font Type, Size and Color
            oGraphics.DrawString
            (
                //Text
            sCaptchaText.Substring(i, 1),
                //Random Font Name and Style
            new Font(aFontNames[oRandom.Next(aFontNames.Length - 1)],
               aFontEmSizes[oRandom.Next(aFontEmSizes.Length - 1)],
               aFontStyles[oRandom.Next(aFontStyles.Length - 1)]),
                //Random Color (Darker colors RGB 0 to 100)
            new SolidBrush(Color.FromArgb(oRandom.Next(0, 100),
               oRandom.Next(0, 100), oRandom.Next(0, 100))),
            x,
            oRandom.Next(10, 40)
            );
            oGraphics.ResetTransform();
        }

        MemoryStream oMemoryStream = new MemoryStream();
        oOutputBitmap.Save(oMemoryStream, System.Drawing.Imaging.ImageFormat.Png);
        byte[] oBytes = oMemoryStream.GetBuffer();

        oOutputBitmap.Dispose();
        oMemoryStream.Close();

        context.Response.BinaryWrite(oBytes);
        context.Response.End();
    }
    public void SetCaptchaText(HttpContext context)
    {
        Random oRandom = new Random();
        int iNumber = oRandom.Next(100000, 999999);
        context.Session["x"] = iNumber.ToString();
    }
    public bool IsReusable
    {
        get
        {
            return false;
        }
    }
 }

=====================================
Call the "CaptchaHandler.ashx" Handler on code page "captcha.aspx", as below:

<body>
    <form id="form1" runat="server">
    <div>
        <img src="Handler.ashx" />
        <asp:Image ID="imgCaptcha" ImageUrl="CaptchaHandler.ashx" runat="server" />
        <asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
        <asp:Label ID="Label1" runat="server" Text=""></asp:Label>
        <asp:Button ID="Button1" runat="server" Text="click" onclick="Button1_Click" />
    </div>
    </form>
</body>

============================================

Valid User to check the Captcha: (captcha.aspx.cs) by adding this code on .cs page

protected void Button1_Click(object sender, EventArgs e)
    {
        if (Session["x"].ToString( ) == TextBox1.Text.Trim( ))
        {
            Label1.Text = "Valid";
        }
        else
        {
            Label1.Text = "Invalid";
        }
        TextBox1.Text = "";
    }

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