How to integrate Captcha in asp.net

Introduction: In this article I have explained how we can integrate Captcha in asp.net.

Description:
In the last article I have explained Auto refresh data in Gridview without loading page whole page in asp.net, How to use SiteMapPath Navigation Control in Asp.net, Encrypt and Decrypt Query String in asp.net, Create multiple Language website in Asp.net and Store Password in Encrypted format to Database in asp.net.

Captcha is mostly used in Sign up and contact us form. I use the Recaptcha library. You can download the Recaptcha library from given link:

http://recaptchanet.codeplex.com/

After download the Recapctha library extract it. You see the option dll for 4.0 or 4.5 frameworks. Take new website, right click on your website and choose Add Reference as shown in snapshot: 

Now click on browse and select the Recaptcha.web.dll. 

You can also add the Captcha control to Toolbox. To use Captcha control you need a public and private key. To get the key go to below given link:

http://www.google.com/recaptcha/whyrecaptcha

Here you are asking for login. Login with your Google/Gmail account. After login you are redirect to create captcha key, enter your domain (e.g. articlemirror.blogspot.in) and select the checkbox to use this on all domains. After that click on Create key button. You have done it. You see a page as shown below:

 

Add caption

Now add the key in web.config file:

<configuration>

       <system.web>

              <compilation debug="true" targetFramework="4.0"/>

       </system.web>

       <appSettings>

              <add key="recaptchaPublicKey" value="Public key"/>

              <add key="recaptchaPrivateKey" value="Private key"/>

       </appSettings>

</configuration>

Add a new webform to website. Register the control on your .aspx page add the following:

<%@ Register Assembly="Recaptcha.Web" Namespace="Recaptcha.Web.UI.Controls" TagPrefix="cc1" %>

If you added the control in toolbox than drag and drop it to page. If not added to toolbox than add the following to page:

<cc1:Recaptcha ID="Recaptcha" runat="server" />

Design the page.aspx as mention below:

<form id="form1" runat="server">

    <div>

    <table align="center"><tr><td>

   <cc1:Recaptcha ID="Recaptcha" runat="server" /></td><td><asp:Label ID="Label1" runat="server" Text=""></asp:Label></td></tr>

   <tr><td>

   <asp:Button ID="btncaptcha" runat="server" Text="Confirm" onclick="btncaptcha_Click" />       

        </td></tr></table>

    </div>

    </form>

On button click write the given code (.aspx.cs) :

using Recaptcha.Web;

protected void btncaptcha_Click(object sender, EventArgs e)

    {

        if (String.IsNullOrEmpty(Recaptcha.Response))

    {

        Label1.Text = "Captcha cannot be empty.";

    }

    else

    {

        RecaptchaVerificationResult verify = Recaptcha.Verify();

        if (verify == RecaptchaVerificationResult.Success)

        {

            Label1.Text = "Captcha Match";

        }

        else

        {

            Label1.Text = "Captcha information not matched";

        }

    }

    }

In VB (.aspx.vb) :

Imports Recaptcha.Web

Protected Sub btncaptcha_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btncaptcha.Click

        If String.IsNullOrEmpty(Recaptcha.Response) Then

            Label1.Text = "Captcha cannot be empty."

        Else

            Dim verify As RecaptchaVerificationResult = Recaptcha.Verify()

            If verify = RecaptchaVerificationResult.Success Then

                Label1.Text = "Captcha Match"

            Else

                Label1.Text = "Captcha information not matched"

            End If

        End If

    End Sub

Now run the project and checked out the result.

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