[b]Create a page with name “Captcha.aspx”
Source:

---

Add the following code to HTML:
IMG height="30" alt="" src=BuildCaptcha.aspx width="80">
asp:TextBox runat="Server" ID="txtCaptcha">

---

Add a button, And In button click add the following

if (Page.IsValid && (txtCaptcha.Text.ToString() ==
Session["RandomStr"].ToString()))
{
Response.Write("Code verification Successful");
}
else
{
Response.Write( "Please enter info correctly");
}

---

Create a new file called “BuildCaptcha.aspx

Source:
1: Bitmap objBMP = new Bitmap(60, 20);

2: Graphics objGraphics = Graphics.FromImage(objBMP);

3: objGraphics.Clear(Color.Wheat);

4: objGraphics.TextRenderingHint = TextRenderingHint.AntiAlias;

5:

6:

7: //' Configure font to use for text

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

9: string randomStr = "";

10: char[] myArray = new char[5];

11: int x;

12:

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

14: Random autoRand = new Random();

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

16: {

17: myArray[x] = System.Convert.ToChar(autoRand.Next(65,90));

18: randomStr += (myArray[x].ToString());

19: }

20:

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

22: Session.Add("RandomStr", randomStr);

23:

24: //' Write out the text

25: objGraphics.DrawString(randomStr, objFont, Brushes.Red, 3, 3);

26:

27: //' Set the content type and return the image

28: Response.ContentType = "image/GIF";

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

30: objFont.Dispose();

31: objGraphics.Dispose();

32: objBMP.Dispose();

Now access captcha.aspx from browser