Developer's Blog- Make life eazy: recaptcha free captcha service for asp.net

Its a common requirement that we require a captcha to be integrated on our page. I would like to mention a free captcha service which can be implemented in integrated on websites.
What is reCaptcha?

reCAPTCHA is a free CAPTCHA service that helps to digitize books, newspapers and old time radio shows.
It’s Free! Yep, reCAPTCHA is free.
It’s Easy. reCAPTCHA is a Web service. As such, adopting it is as simple as adding
a few lines of code on your site.
It’s Accessible. reCAPTCHA has an audio test that allows blind people to freely
navigate your site.
It’s Secure. Most other CAPTCHA implementations can be easily broken.
It’s Popular. Over 100,000 sites use reCAPTCHA, including household names like Facebook, Ticketmaster, and Craigslist.
Whenever uses input data in reCaptcha control, they actually help digitizing books.

Moreover is very easy to integrate reCaptcha in our websites. Below are the steps
which are required to integrate it into a ASP.NET page.
Steps to Integrate reCaptcha in ASP.NET

Register for a reCaptcha key : As a first step we need to register for recaptcha keys. Navigate to Get reCaptcha URL to signup for the keys. After we register for the keys, we get a public and private keys which we need to use in our asp.net page. By default all keys work on localhost as well.
Download reCaptcha library for ASP.NET: Download the dll file from here. Also add the reference to the dll in the asp.net project.
Add reCaptcha widget on ASP.NET page : Insert the reCAPTCHA control into the form you wish to protect by adding the following code snippets:
- At the top of the aspx page, insert this:
  
  1
  2
  <%@ register
  tagprefix="recaptcha" namespace="Recaptcha" assembly="Recaptcha" %>
- Then insert the reCAPTCHA control inside of the form tag:
  
  1
  2
  <recaptcha:recaptchacontrol id="recaptcha" runat="server" publickey="your_public_key"
  privatekey="your_private_key" />
Make sure you use ASP.NET validation to validate your form (you should check Page.IsValid on submission).

As an example I created a ASP.NET page whose markup and code behind code looks as given below:
Markup:

<%@  Page Language="C#" AutoEventWireup="true"  CodeBehind="RecaptchaPage.aspx.cs"  Inherits="ContosoUniversity.RecaptchaPage" %>
<%@ Register TagPrefix="recaptcha" Namespace="Recaptcha" Assembly="Recaptcha" %>
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title>title>
head>
<body>
    <form id="form1" runat="server">
    <div>
     <asp:Label Visible="true" ID="lblResult" runat="server" />
     <recaptcha:RecaptchaControl
              ID="recaptcha"
              runat="server"
              Theme="red"
              PublicKey="6LcoxcASAAAAAGAQQz_xOTk4-ALrRQri_Cf8AuhL"
              PrivateKey="6LcoxcASAAAAALfZhquqene7_4bTrzmuqHBrkuk0"
              />
          <asp:Button ID="btnSubmit" runat="server" Text="Submit" OnClick="btnSubmit_Click" />
    div>
    form>
body>
html>

Code-behind

public partial class RecaptchaPage : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
    }
    protected void btnSubmit_Click(object sender, EventArgs e)
    {
        if (Page.IsValid)
        {
          lblResult.Text = "Captcha sucessfull!";
          lblResult.ForeColor = System.Drawing.Color.Green;
        }
        else
        {
          lblResult.Text = "Incorrect";
          lblResult.ForeColor = System.Drawing.Color.Red;
        }
    }
}