Captcha image in C#.NET

Captcha image in C#.NET

What Captcha stand for?

Completely Automated Public Turing test to tell Computers and Humans Apart. The Captcha technology help you to make sure your site is reasonably secure against automated attacks.

Write the following code in a class named Captcha:

public class Captcha
{
    //make the captcha image for text
    public Bitmap MakeCaptchaImage(string txt, int width, int hight, string fontFamilyName)
    {
        //make the bitmap and the associated Graphics object
        Bitmap bm = new Bitmap(width, hight);
        Graphics gr = Graphics.FromImage(bm);
        gr.SmoothingMode = SmoothingMode.HighQuality;
        RectangleF recF = new RectangleF(0, 0, width, hight);
        Brush br;
        br = new HatchBrush(HatchStyle.SmallConfetti, Color.LightGray, Color.White);
        gr.FillRectangle(br, recF);
        SizeF text_size;
        Font the_font;
        float font_size = hight + 1;
        do
        {
            font_size -= 1;
            the_font = new Font(fontFamilyName, font_size, FontStyle.Bold, GraphicsUnit.Pixel);
            text_size = gr.MeasureString(txt, the_font);
        }
        while ((text_size.Width > width) || (text_size.Height > hight));
        // Center the text.
        StringFormat string_format = new StringFormat();
        string_format.Alignment = StringAlignment.Center;
        string_format.LineAlignment = StringAlignment.Center;

        // Convert the text into a path.
        GraphicsPath graphics_path = new GraphicsPath();
        graphics_path.AddString(txt, the_font.FontFamily, 1, the_font.Size, recF, string_format);

        //Make random warping parameters.
        Random rnd = new Random();
        PointF[] pts = { new PointF((float)rnd.Next(width) / 4, (float)rnd.Next(hight) / 4), new PointF(width - (float)rnd.Next(width) / 4, (float)rnd.Next(hight) / 4), new PointF((float)rnd.Next(width) / 4, hight - (float)rnd.Next(hight) / 4), new PointF(width - (float)rnd.Next(width) / 4, hight - (float)rnd.Next(hight) / 4) };
        Matrix mat = new Matrix();
        graphics_path.Warp(pts, recF, mat, WarpMode.Perspective, 0);

        // Draw the text.
        br = new HatchBrush(HatchStyle.LargeConfetti, Color.LightGray, Color.DarkGray);
        gr.FillPath(br, graphics_path);

        // Mess things up a bit.
        int max_dimension = System.Math.Max(width, hight);
        for (int i = 0; i <= (int)width * hight / 30; i++)
        {
            int X = rnd.Next(width);
            int Y = rnd.Next(hight);
            int W = (int)rnd.Next(max_dimension) / 50;
            int H = (int)rnd.Next(max_dimension) / 50;
            gr.FillEllipse(br, X, Y, W, H);
        }
        for (int i = 1; i <= 5; i++)
        {
            int x1 = rnd.Next(width);
            int y1 = rnd.Next(hight);
            int x2 = rnd.Next(width);
            int y2 = rnd.Next(hight);
            gr.DrawLine(Pens.DarkGray, x1, y1, x2, y2);
        }
        for (int i = 1; i <= 5; i++)
        {
            int x1 = rnd.Next(width);
            int y1 = rnd.Next(hight);
            int x2 = rnd.Next(width);
            int y2 = rnd.Next(hight);
            gr.DrawLine(Pens.LightGray, x1, y1, x2, y2);
        }
        graphics_path.Dispose();
        br.Dispose();
        the_font.Dispose();
        gr.Dispose();
        return bm;
    }
}

Usage:

Captcha oCaptcha = new Captcha();
Random rnd = new Random();
string[] s = { "0", "1", "2", "3", "4", "5", "6", "7", "8", "9", "a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n", "p", "q", "r", "s", "t", "u", "v", "w", "x", "y", "z" };
int i;
StringBuilder sb = new StringBuilder(4);
for (i = 0; i <= 4; i++)
{
    sb.Append(s[rnd.Next(1, s.Length)]);
}
Bitmap bm = oCaptcha.MakeCaptchaImage(sb.ToString(), 200, 100, "Arial");
string url = Server.MapPath("~/Images/Captcha.bmp");
bm.Save(url);
Image1.ImageUrl = "~/Images/Captcha.bmp";

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Comments (5)

  • el3tafy Reply

    tslm dma3’k bgd
    ana kont m7tag a3rf el fekra bta3ha mn zmaaan
    wz amr saafan mosh hat2dr t3’md 3neek

    July 17, 2008 at 11:46 AM
  • Chris Par Reply

    Nice article! However, the codes are not properly placed. It is a good idea to put it into Code Snippet.

    You can download Microsoft Live Writer to help you with it. I’m using it for my blog too. Nice tool.

    Regards,
    Chris

    August 11, 2008 at 5:56 PM
    • Amr Saafan Reply

      Thank you Chris for your good advice.

      August 12, 2008 at 9:22 AM
  • Anonymous Reply

    ((text_size.Width > width)(text_size.Height > height))

    is missing the || (Or operator) in the C# sample. Probably an encoding anomaly.

    December 4, 2009 at 6:38 PM
    • Amr Saafan Reply

      Yes, true the || (Or operator) was missing and I updated the post now. Thank you.

      December 7, 2009 at 1:01 PM

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