Introduction

Here I create a Captcha Code with JavaScript.
Step 1
In the (.aspx) page we write the following Code:
  1. <%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="_Default" %>
  2. <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
  3. <html xmlns="http://www.w3.org/1999/xhtml">
  4. <head id="Head1" runat="server">
  5. <title></title>
  6. <script language="javascript">
  7. var a = 49, b = 65;
  8. var c = 100;
  9. var d = 70;
  10. function show() {
  11. if (a == 57) {
  12. a = 49;
  13. }
  14. var main = document.getElementById('txt1');
  15. var a1 = String.fromCharCode(a);
  16. var b1 = String.fromCharCode(b);
  17. var c1 = String.fromCharCode(c);
  18. var d1 = String.fromCharCode(d);
  19. main.value = a1 + b1 + c1 + d1;
  20. a = a + 1;
  21. b = b + 1;
  22. c = c + 1;
  23. d = d + 1;
  24. }
  25. </script>
  26. <style type="text/css">
  27. #form1
  28. {
  29. height: 95px;
  30. }
  31. </style>
  32. </head>
  33. <body>
  34. <form id="form1" runat="server">
  35. <div>
  36. <input type="text" id="txt1" runat="server"
  37. style="border-style: none; border-color: inherit; border-width: medium; background-color:black; color:red; font-family: 'Curlz MT'; font-size: x-large; font-weight: bold; font-variant: normal; letter-spacing: 10pt; width: 120px; background-image: url('glitter_background_b4.gif');"
  38. value="5AbD" />
  39. <input type="button" onclick="show()" value="Change" />
  40. </div>
  41. <asp:TextBox ID="txtverification" runat="server"></asp:TextBox>
  43. <asp:Button ID="Button1" runat="server" Text="Verification"
  44. onclick="Button1_Click" />
  46. <asp:Label ID="lblmsg" runat="server" Font-Bold="True" ForeColor="Red"></asp:Label>
  47. </form>
  48. </body>
  49. </html>
Step 2
In the (.cs) page I write the following code for verification:
  1. protected void Button1_Click(object sender, EventArgs e)
  2. {
  3. if (txtverification.Text == txt1.Value)
  4. {
  5. lblmsg.Text = "Successful";
  6. }
  7. else
  8. {
  9. lblmsg.Text = "Failure";
  10. }
  11. }