<%@ WebHandler Language="C#" Class="Captcha" %>

using System;
using System.Web;
using System.Drawing.Drawing2D;
using System.Drawing;

public class Captcha : IHttpHandler, System.Web.SessionState.IRequiresSessionState
{

    public void ProcessRequest(HttpContext context)
    {
        //string cvalue = context.Request.QueryString["cvalue"].ToString();
        string number = RandomString(4);
        context.Session["CaptchCode"] = number;
        string cvalue = number;

        int iHeight = 35;
        int iWidth = 100;
        Random oRandom = new Random();

        int[] aBackgroundNoiseColor = new int[] { 255, 255, 255 };
        int[] aTextColor = new int[] { 0, 0, 0 };
        int[] aFontEmSizes = new int[] { 15, 15, 15, 15, 15 };

        string[] aFontNames = new string[]
        {
         "Arial"
        };
        FontStyle[] aFontStyles = new System.Drawing.FontStyle[]
        {  
         FontStyle.Bold
        };
        HatchStyle[] aHatchStyles = new System.Drawing.Drawing2D.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 = cvalue;

        //Creates an output Bitmap
        Bitmap oOutputBitmap = new Bitmap(iWidth, iHeight, System.Drawing.Imaging.PixelFormat.Format24bppRgb);
        Graphics oGraphics = Graphics.FromImage(oOutputBitmap);
        oGraphics.TextRenderingHint = System.Drawing.Text.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(255, 255)),
            (oRandom.Next(255, 255)), (oRandom.Next(255, 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 + 5;
            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, 0),
               oRandom.Next(0, 0), oRandom.Next(0, 0))),
            x,
            oRandom.Next(10, 10)
            );
            oGraphics.ResetTransform();
        }

        System.IO.MemoryStream oMemoryStream = new System.IO.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 bool IsReusable
    {
        get
        {
            return false;
        }
    }
    public static string RandomString(int length)
    {
        var chars = "0123456789";
        var stringChars = new char[length];
        var random = new Random();
        for (int i = 0; i < stringChars.Length; i++)
        {
            stringChars[i] = chars[random.Next(chars.Length)];
        }
        var finalString = new String(stringChars);
        return finalString;
    }

}