Simple Captcha Using C#

I was trying to find a solution to block spammers adding data to our database using C#. This is the quick solution I found.

First create an image tag in the webform that has the submit form.

<IMG height="30" alt="" src="Turing.aspx" width="80">

As you see the source for the picture will be a file called "Turing.aspx".

Later create the webform "Turing.aspx" with the code below

public class Turing1 : System.Web.UI.Page
{

private void Page_Load(object sender, System.EventArgs e)
{

Bitmap objBMP =new System.Drawing.Bitmap(60,20);

Graphics objGraphics = System.Drawing.Graphics.FromImage(objBMP);

objGraphics.Clear(Color.Green);

objGraphics.TextRenderingHint = TextRenderingHint.AntiAlias;

//’ Configure font to use for text

Font objFont = new Font("Arial", 8, FontStyle.Bold);

string randomStr="";

int[] myIntArray = new int[5] ;

int x;

//That is to create the random # and add it to our string

Random autoRand = new Random();

for (x=0;x<5;x++)

{
myIntArray[x] = System.Convert.ToInt32 (autoRand.Next(0,9));

randomStr+= (myIntArray[x].ToString ());

}

//This is to add the string to session cookie, to be compared later

Session.Add("randomStr",randomStr);

//’ Write out the text

objGraphics.DrawString(randomStr, objFont, Brushes.White, 3, 3);

//’ Set the content type and return the image

Response.ContentType = "image/GIF";

objBMP.Save(Response.OutputStream, ImageFormat.Gif);

objFont.Dispose();

objGraphics.Dispose();

objBMP.Dispose();
}

}

And this is the code for the submit button on the main form

private void btnSubmit_ServerClick(object sender, System.EventArgs e)

{

if (Page.IsValid && (txtTuring.Value.ToString () ==Session["randomStr"].ToString ()))

{
// The Code to insert data
}
else

{

Label1.Text ="Please enter info correctly";

}
}

4) Finally make sure you add the related System libraries,

using System.Drawing;

using System.Drawing.Text;

using System.Drawing.Imaging;

in front of the class and this is it.

Hope this helps.

Regards

http://www.ottawatutors.com

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