Using ASP.NET to Create Captcha Code

We must first comprehend “What is a Captcha code?” and “Why do we use them?” before moving on to the issue. The majority of websites include a Captcha validation.

What is the Captcha code?

A Captcha code is simply a combination of some characters and numbers like “Alk13” or “aTu2eP” etc.

Why do we use them?

We use them for validating that the client browser window really has a human typing into it.

Ok, let’s get to the topic i.e. creating your own Captcha code in ASP.Net.

Step 1

Go to Visual Studio and create a new project (web site or web application) say “CaptchCode”.

Step 2

Now add a new page into your application say “ShowCaptcha.aspx” and add this code into the source for the page:

<div>
<table>
  <tr>
    <td>
      <asp:Image ID="imgCaptcha" runat="server" ImageUrl="~/CreateCaptcha.aspx?New=1"/>
     </td>
   </tr>
   <tr>
    <td>
      <asp:TextBox ID="txtCaptcha" runat="server"></asp:TextBox>
     </td>
    </tr>
    <tr>
     <td>
       <asp:Label ID="lblMessage" runat="server"></asp:Label>
      </td>
     </tr>
     <tr>
      <td>
 <asp:Button ID="btnCaptcha" runat="server" Text="Validate Cpatcha Code" onclick="btnCaptcha_Click" />
       </td>
       </tr>
     </table>
    </div>

Note: Here I am given the ImageUrl=”~/CreateCaptcha.aspx?New=1″ of the image control. In CreateCaptcha.aspx we will write the code for creating the Captcha code.

Step 3

Now add a new page into your application “CreateCaptcha.aspx” and create the following methods in its .cs file:

  /// <summary>
/// method for create captcha image
/// </summary>
 private void CreateCaptchaImage()
{  
 code = GetRandomText(); 
 Bitmap bitmap = new Bitmap(200, 60, System.Drawing.Imaging.PixelFormat.Format32bppArgb);
 Graphics g = Graphics.FromImage(bitmap);
 Pen pen = new Pen(Color.Yellow);
 Rectangle rect = new Rectangle(0, 0, 200, 60);
 SolidBrush blue = new SolidBrush(Color.CornflowerBlue);
 SolidBrush black = new SolidBrush(Color.Black);
 int counter = 0;
 g.DrawRectangle(pen, rect);
 g.FillRectangle(blue, rect);
 
 for (int i = 0; i < code.Length; i++)
 {
    g.DrawString(code[i].ToString(), new Font("Tahoma", 10 + rand.Next(15, 20), FontStyle.Italic), black, new PointF(10 + counter, 10));
   counter += 28;
 }
 DrawRandomLines(g);           
 bitmap.Save(Response.OutputStream, ImageFormat.Gif);
 g.Dispose();
 bitmap.Dispose();
 
}
 
/// <summary>
/// Method for drawing lines
/// </summary>
/// <param name="g"></param>
private void DrawRandomLines(Graphics g)
{
   SolidBrush yellow = new SolidBrush(Color.Yellow);
   for (int i = 0; i < 20; i++)
   {g.DrawLines(new Pen(yellow, 1), GetRandomPoints());}
 
}
 
/// <summary>
/// method for gettting random point position
/// </summary>
/// <returns></returns>
private Point[] GetRandomPoints()
{
  Point[] points = { new Point(rand.Next(0, 150), rand.Next(1, 150)), new    Point(rand.Next(0, 200), rand.Next(1, 190)) };
  return points;
}
   
/// <summary>
/// Method for generating random text of 5 cahrecters as captcha code
/// </summary>
/// <returns></returns>
private string GetRandomText()
{
  StringBuilder randomText = new StringBuilder();           
  string alphabets = "012345679ACEFGHKLMNPRSWXZabcdefghijkhlmnopqrstuvwxyz";
  Random r = new Random();
  for (int j = 0; j <= 5; j++)
  {randomText.Append(alphabets[r.Next(alphabets.Length)]);}
    Session["CaptchaCode"] = randomText.ToString();
     return Session["CaptchaCode"] as String;
  }

Step 4

To validate the Captcha code in the “ShowCaptcha.aspx.cs” page:

protected void btnCaptcha_Click(object sender, EventArgs e)
{
   //imgCaptcha.ImageUrl = "~/CreateCaptcha.aspx?New=0";
  if (Session["CaptchaCode"] != null && txtCaptcha.Text == Session["CaptchaCode"].ToString())
  {
     lblMessage.ForeColor = Color.Green;
     lblMessage.Text = "Captcha code validated successfully!!";
  }
  else
  {
   lblMessage.ForeColor = Color.Red;
   lblMessage.Text = "Captcha code is wrong!!";
  }
}

I hope this article will be helpful for you. Happy Coding!!

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