Simple Captcha Using C#

Sunday Dec 16th 2012 by Oguz Altuncu

simple captcha

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.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
//' 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);
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
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