Simple Captcha with ASP.NET

Introduction

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

1. 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”.

2. 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();
      }
   }

3. 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";
       }
   }