How to create captcha Image (asp.net) CaptchaImage.cs

 using System;

using System.Data;

using System.Configuration;

using System.Web;

using System.Web.Security;

using System.Web.UI;

using System.Web.UI.WebControls;

using System.Web.UI.WebControls.WebParts;

//using System.Web.UI.aspxlControls;

using System.Drawing;

using System.Drawing.Drawing2D;

public class CatpchaImage

{

    public static string SESSION_CAPTCHA = "CAPTCHA";

    

    const int default_width = 140;

    const int default_height = 40;

    protected Bitmap result = null;

    public int Width;

    public int Height;

    public CatpchaImage()

    {

        InitBitmap(default_width, default_height);

        rnd = new Random();

    }

    public CatpchaImage(int width, int height)

    {

        InitBitmap(width, height);

    }

    protected void InitBitmap(int width, int height)

    {

        result = new Bitmap(width, height);

        Width = width;

        Height = height;

        rnd = new Random();

    }

    public PointF Noise(PointF p, double eps)

    {

        p.X = Convert.ToSingle(rnd.NextDouble() * eps * 2 - eps) + p.X;

        p.Y = Convert.ToSingle(rnd.NextDouble() * eps * 2 - eps) + p.Y;

        return p;

    }

    public PointF Wave(PointF p, double amp, double size)

    {

        p.Y = Convert.ToSingle(Math.Sin(p.X / size) * amp) + p.Y;

        p.X = Convert.ToSingle(Math.Sin(p.X / size) * amp) + p.X;

        return p;

    }

    public GraphicsPath RandomWarp(GraphicsPath path)

    {

        // Add line //

        int PsCount = 10;

        PointF[] curvePs = new PointF[PsCount * 2];

        for (int u = 0; u < PsCount; u++)

        {

            curvePs[u].X = u * (Width / PsCount);

            curvePs[u].Y = Height / 2;

        }

        for (int u = PsCount; u < (PsCount * 2); u++)

        {

            curvePs[u].X = (u - PsCount) * (Width / PsCount);

            curvePs[u].Y = Height / 2 + 2;

        }

      

        double eps = Height * 0.05;

        double amp = rnd.NextDouble() * (double)(Height / 3);

        double size = rnd.NextDouble() * (double)(Width / 4) + Width / 8;

        double offset = (double)(Height / 3);

        PointF[] pn = new PointF[path.PointCount];

        byte[] pt = new byte[path.PointCount];

        GraphicsPath np2 = new GraphicsPath();

        GraphicsPathIterator iter = new GraphicsPathIterator(path);

        for (int i = 0; i < iter.SubpathCount; i++)

        {

            GraphicsPath sp = new GraphicsPath();

            bool closed;

            iter.NextSubpath(sp, out closed);

            Matrix m = new Matrix();

            m.RotateAt(Convert.ToSingle(rnd.NextDouble() * 30 - 15), sp.PathPoints[0]);

            m.Translate(-1 * i, 0);//uncomment

            sp.Transform(m);

            np2.AddPath(sp, true);

        }

        for (int i = 0; i < np2.PointCount; i++)

        {

            //pn[i] = Noise( path.PathPoints[i] , eps);

            pn[i] = Wave(np2.PathPoints[i], amp, size);

            pt[i] = np2.PathTypes[i];

        }

        GraphicsPath newpath = new GraphicsPath(pn, pt);

        return newpath;

    }

    Random rnd;

    public string DrawNumbers(int len)

    {

        string str = "";

        string possible = "ABCDEFGHJKLMNPQRSTUVWXYZ23456789abcdfghjkmnpqrstvwxyz";

        char ch='A';

        for (int i = 0; i < len; i++)

        {           

            ch=possible[rnd.Next(0, possible.Length -1)];

            str = str + ch.ToString();

        }

        DrawText(str);

        return str;

    }

    public void DrawText(string aText)

    {

        Graphics g = Graphics.FromImage(result);

        int startsize = Height;

        Font f = new Font("Verdana", startsize, FontStyle.Bold, GraphicsUnit.Pixel);

        do

        {

            f = new Font("Verdana", startsize, GraphicsUnit.Pixel);

            startsize--;

        } while ((g.MeasureString(aText, f).Width >= Width) || (g.MeasureString(aText, f).Height >= Height));

        SizeF sf = g.MeasureString(aText, f);

        int width = Convert.ToInt32(sf.Width);

        int height = Convert.ToInt32(sf.Height);

        int x = Convert.ToInt32(Math.Abs((double)width - (double)Width) * rnd.NextDouble());

        int y = Convert.ToInt32(Math.Abs((double)height - (double)Height) * rnd.NextDouble());

        //////// Paths ///

        GraphicsPath path = new GraphicsPath(FillMode.Alternate);

        FontFamily family = new FontFamily("Verdana");      

        int fontStyle = (int)(FontStyle.Regular);

        float emSize = f.Size;

        Point origin = new Point(x, y);

        StringFormat format = StringFormat.GenericDefault;

        path.AddString(aText, family, fontStyle, emSize, origin, format);

       

        g.TextRenderingHint = System.Drawing.Text.TextRenderingHint.AntiAlias;

        Rectangle rect = new Rectangle(0, 0, Width, Height);

        g.FillRectangle(new System.Drawing.Drawing2D.LinearGradientBrush(rect, Color.White, Color.White, 0f), rect);

        g.SmoothingMode = SmoothingMode.HighQuality;

        Color noiseCol = Color.FromArgb(100, 120, 180);

        Pen p = new Pen(noiseCol);

        

        

        /* generate random dots in background */

      for( int i=0; i<(Width*Height)/3; i++ ) {

          g.FillEllipse(Brushes.Blue, rnd.Next(0, Width), rnd.Next(0, Height), 1, 1);

      }

        /*noise ends here*/

        /* generate random lines in background */

      for( int i=0; i<(Width*Height)/150; i++ ) {

         g.DrawLine(p,rnd.Next(0,Width), rnd.Next(0,Height), rnd.Next(0,Width), rnd.Next(0,Height));

      }

       

      Color textColor = Color.FromArgb(20, 40, 100);

      g.FillPath(new SolidBrush(textColor), path);

      

      g.Dispose();

    }

    public Bitmap Result

    {

        get

        {

            return result;

        }

    }

   

}