ASP.NET Ajax CAPTCHA VB.NET Code Sample (BotDetect v3.0; deprecated)

The ASP.NET Ajax Captcha sample project shows how to use BotDetect CAPTCHA within an ASP.NET Ajax UpdatePanel. The basic code used to add Captcha protection to the page is the same as in regular ASP.NET forms.

First Time Here?

Check the BotDetect ASP.NET WebForms Captcha Quickstart for key integration steps.

However, some additional work is required if BotDetect is not visible on the first page load, but gets added to the page dynamically. Since BotDetect can't automatically add required stylesheet and client-side script includes to the page if it's not visible on the first page load, they can be added manually.

In this sample, the BotDetect stylesheet include is added to the Default.aspx page header, while the script include and the BotDetect initialization script are registered in the code-behind.

  • C#
  • VB.NET

ASP.NET Ajax 4.5 / Visual Studio 2013 / Visual Studio 2012 / .NET 4.5

By default, the .NET 4.5 VB.NET version of the ASP.NET Ajax Captcha sample project is installed at:
C:\Program Files\Lanapsoft\BotDetect 3 CAPTCHA Component\Asp.Net\v4.5\WebApp\AspNetAjaxCaptchaSample\VBNet

You can also run it from the BotDetect Start Menu:
Programs > Lanapsoft > BotDetect 3 CAPTCHA Component > ASP.NET > DotNET 4.5 Web Applications > Run

Default.aspx

<%@ Page Language="VB" AutoEventWireup="true"  CodeFile="Default.aspx.vb" 
  Inherits="_Default" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" 
  "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">

<html xmlns="http://www.w3.org/1999/xhtml" >
<head id="Head1" runat="server">
  <title>BotDetect CAPTCHA ASP.NET Ajax Sample</title>
  <link type="text/css" rel="Stylesheet" href="StyleSheet.css" />
  <!-- ensure the BotDetect layout stylesheet is included -->
  <link type="text/css" rel="Stylesheet" 
    href="BotDetectCaptcha.ashx?get=layoutStylesheet" />
</head>
<body>
  <form id="form1" runat="server">
  <h1>BotDetect CAPTCHA ASP.NET Ajax Sample</h1>
  <fieldset>
    <legend>CAPTCHA Validation</legend>
    <asp:ScriptManager ID="ScriptManager1" runat="server" />
    <asp:UpdatePanel ID="CaptchaUpdatePanel" runat="server" UpdateMode="Conditional">
      <ContentTemplate>
        <asp:Panel ID="Panel1" runat="server">
          <h3>Step 1</h3>
          <p class="prompt">The first screen doesn't contain 
          BotDetect yet. After you click "Next", Captcha 
          protection will be shown using an ASP.NET Ajax 
          partial postback.</p>
          <asp:Button ID="Button1" runat="server" Text="Next" 
            OnClick="Button1_Click" />
        </asp:Panel>
        <asp:Panel ID="Panel2" runat="server" Visible="false">
          <h3>Step 2</h3>
          <p class="prompt"><label for="CaptchaCodeTextBox">Retype the characters 
            from the picture:</label></p>
          <BotDetect:Captcha ID="SampleCaptcha" runat="server" />
          <div class="validationDiv">
            <asp:TextBox ID="CaptchaCodeTextBox" runat="server"></asp:TextBox>
            <asp:Button ID="ValidateCaptchaButton" runat="server" 
              OnClick="ValidateCaptchaButton_Click" />
            <asp:Label ID="CaptchaIncorrectLabel" runat="server" CssClass="incorrect">
            </asp:Label>
          </div>
        </asp:Panel>
      </ContentTemplate>
    </asp:UpdatePanel>
    </fieldset>
  </form>
</body>
</html>

To showcase the most complex ASP.NET Ajax workflow, BotDetect is added to a Panel within an UpdatePanel, and added to the form dynamically after an ASP.NET Ajax partial postback.

Since BotDetect wasn't visible on the page during the first load, it couldn't add the Captcha stylesheet and script library to the page. Adding them during the partial page update doesn't always work, so we also included the BotDetect stylesheet in the page header.

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Default.aspx.vb

Partial Class _Default
    Inherits System.Web.UI.Page

    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.
    EventArgs) Handles Me.PreRender
        ' initial page setup
        If Not IsPostBack Then
            ' set control text
            ValidateCaptchaButton.Text = "Validate"
            CaptchaIncorrectLabel.Text = "Incorrect!"

            CaptchaIncorrectLabel.Visible = False
        End If

        ' setup client-side input processing
        SampleCaptcha.UserInputClientID = CaptchaCodeTextBox.ClientID
    End Sub


    Protected Sub Button1_Click(ByVal sender As Object, ByVal e As 
    System.EventArgs) Handles Button1.Click
        Panel1.Visible = False
        Panel2.Visible = True

        CaptchaIncorrectLabel.Visible = False

        ' ensure the BotDetect client scripts are added to the page
        IncludeBotDetectScripts()
    End Sub


    Protected Sub IncludeBotDetectScripts()
        ScriptManager.RegisterClientScriptInclude( _
            Me.Page, _
            Me.GetType(), _
            "BotDetect_Include", _
            SampleCaptcha.CaptchaControl.Urls.ClientScriptIncludeUrl)

        ScriptManager.RegisterClientScriptBlock( _
            Me.Page, _
            Me.GetType(), _
            "BotDetect_Init", _
            SampleCaptcha.CaptchaControl.ClientScriptInitializationFragment, _
            False)
    End Sub


    Protected Sub ValidateCaptchaButton_Click(ByVal sender As Object, 
    ByVal e As System.EventArgs) Handles ValidateCaptchaButton.Click
        ' validate the Captcha to check we're not dealing with a bot
        Dim code As String, isHuman As Boolean
        code = CaptchaCodeTextBox.Text.Trim().ToUpper()
        isHuman = SampleCaptcha.Validate(code)
        CaptchaCodeTextBox.Text = "" ' clear previous user input

        If isHuman Then
            CaptchaIncorrectLabel.Visible = False

            Panel1.Visible = True
            Panel2.Visible = False
        Else
            CaptchaIncorrectLabel.Visible = True
        End If
    End Sub

End Class

To ensure BotDetect client-side scripts are added to the page when they are needed, we call the IncludeBotDetectScripts() helper before the second panel becomes visible. The rest of the class contains the usual BotDetect setup and validation code, adjusted for the two-panel workflow.

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Web.config

<?xml version="1.0"?>
<!--
  For more information on how to configure your ASP.NET application, please visit
  http://go.microsoft.com/fwlink/?LinkId=169433
  -->
<configuration>
  <configSections>
    <section name="botDetect" requirePermission="false" 
      type="BotDetect.Configuration.BotDetectConfigurationSection, BotDetect"/>
  </configSections>
  <appSettings>
    <add key="aspnet:UseTaskFriendlySynchronizationContext" value="true"/>
    <add key="ValidationSettings:UnobtrusiveValidationMode" value="None"/>
  </appSettings>
  <system.web>
    <httpHandlers>
      <!-- Register the HttpHandler used for BotDetect Captcha requests -->
      <add verb="GET" path="BotDetectCaptcha.ashx" 
        type="BotDetect.Web.CaptchaHandler, BotDetect"/>
    </httpHandlers>
    <!-- Register a custom SessionIDManager for BotDetect Captcha requests -->
    <sessionState mode="InProc" cookieless="AutoDetect" timeout="20" 
      sessionIDManagerType="BotDetect.Web.CustomSessionIdManager, BotDetect"/>
    <!-- Session state is required for BotDetect storage; you can also turn if off 
      globally and only enable for BotDetect-protected pages if you prefer -->
    <pages controlRenderingCompatibilityVersion="4.5" enableSessionState="true">
      <controls>
        <!-- Register the BotDetect tag prefix for easier use in all pages -->
        <add assembly="BotDetect" namespace="BotDetect.Web.UI" tagPrefix="BotDetect"/>
      </controls>
    </pages>
    <compilation debug="false" targetFramework="4.5"/>
    <httpRuntime requestValidationMode="4.5" targetFramework="4.5" 
      encoderType="System.Web.Security.AntiXss.AntiXssEncoder, System.Web, 
        Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a"/>
    <machineKey compatibilityMode="Framework45"/>
  </system.web>
  <system.webServer>
    <validation validateIntegratedModeConfiguration="false"/>
    <handlers>
      <!-- Register the HttpHandler used for BotDetect Captcha requests (IIS 7.0+) -->
      <remove name="BotDetectCaptchaHandler"/>
      <add name="BotDetectCaptchaHandler" preCondition="integratedMode" verb="GET" 
        path="BotDetectCaptcha.ashx" type="BotDetect.Web.CaptchaHandler, BotDetect"/>
    </handlers>
  </system.webServer>
  <botDetect>
    <captchaImage>
      <helpLink enabled="true" mode="image" />
    </captchaImage>
  </botDetect>
</configuration>

There are several BotDetect-related changes in the web.config file, including Captcha HttpHandler registration, ASP.NET Session state configuration, and BotDetect tag prefix registration.

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ASP.NET Ajax 4.0 / Visual Studio 2010 / .NET 4.0

By default, the .NET 4.0 VB.NET version of the ASP.NET Ajax Captcha sample project is installed at:
C:\Program Files\Lanapsoft\BotDetect 3 CAPTCHA Component\Asp.Net\v4.0\WebApp\AspNetAjax40CaptchaSample\VBNet

You can also run it from the BotDetect Start Menu:
Programs > Lanapsoft > BotDetect 3 CAPTCHA Component > ASP.NET > DotNET 4.0 Web Applications > Run

The Visual Studio 2010 / .NET 4.0 source has no essential differences from the Visual Studio 2013 / Visual Studio 2012 / .NET 4.5 source.

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ASP.NET Ajax 1.0 / Visual Studio 2008 / .NET 3.5

By default, the .NET 3.5 VB.NET version of the ASP.NET Ajax Captcha sample project is installed at:
C:\Program Files\Lanapsoft\BotDetect 3 CAPTCHA Component\Asp.Net\v3.5\WebApp\AspNetAjax10CaptchaSample\VBNet

You can also run it from the BotDetect Start Menu:
Programs > Lanapsoft > BotDetect 3 CAPTCHA Component > ASP.NET > DotNET 3.5 Web Applications > Run

The Visual Studio 2008 / .NET 3.5 source has no essential differences from the Visual Studio 2013 / Visual Studio 2012 / .NET 4.5 source.

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Please Note

The information on this page is out of date and applies to a deprecated version of BotDetect™ CAPTCHA (v3.0).

An up-to-date equivalent page for the latest BotDetect Captcha release (v4) is BotDetect v4 Captcha documentation index.

General information about the major improvements in the current BotDetect release can be found at the What's New in BotDetect v4.0 page.

© Captcha, Inc. 2004-2025. All rights reserved.

BotDetect, BotDetect CAPTCHA, Lanap, Lanap CAPTCHA, Lanap BotDetect, Lanap BotDetect CAPTCHA, Lanapsoft, Lanapsoft CAPTCHA, Lanapsoft BotDetect, Lanapsoft BotDetect CAPTCHA, and Lanap Software are trademarks of Captcha, Inc. All other product, brand, and company names are mentioned for identification purposes only and are trademarks or registered trademarks of their respective owners.

Captcha, Inc. -- formerly: Lanapsoft, Inc. / Lanap, Inc.