Simple Captcha with ASP.Net

I was trying to find a solution to block spammers adding data to our 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";
   }
   }