Ported over from our ASP Classic Code«

No Captcha ReCaptcha 2.0 with ASP.NET using C# is easy to set up and use with this code to stop bots and minimize spammers.
Google's new No Captcha reCAPTCHA 2.0 with ASP.NET integration will allow everyone running C# for their websites to add this new tool to their arsenal to help combat bots and slow down spammers.

Shahid Shaikh from codeforgeek.com« (Article is no longer available.)
His response got me pointed in the right direction.

Live Lessons Example - No Captcha ReCaptcha 2.0 with ASP.NET (C# Version)

You will need the new reCAPTCHA 2.0 Site Key.
Go here: https://www.google.com/recaptcha/admin«.
Add a new Site Key for your website.
For local testing, you will have to test with
127.0.0.1/Load.aspx
It will not work with a static IP Address or with localhost anymore.

[Load.aspx]

CFFCS | CarrzSynEdit: | ASP.NET (VB/C#)

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Load.aspx.cs" Inherits="Load" %>
<!DOCTYPE html>
<html xmlns="http:'www.w3.org/1999/xhtml">
<head runat="server">
    <title></title>
<script src='https:'www.google.com/recaptcha/api.js'></script>
</head>
<body>
<form id="form1" runat="server">
<label>Name</label>
<asp:TextBox ID="name" runat="server"></asp:TextBox>
<%
'You will need the new reCAPTCHA 2.0 Site Key for this.
'Go here: https:'www.google.com/recaptcha/admin
'And add a new Site Key for your website.
'For local testing, you will have to test with
'local/site.asp
'127.0.1/site.asp
'It will not work with a static IP Address as I would prefer.
%>
        <div class="g-recaptcha" data-sitekey="6LeGzQATAAAAAGglcdHMRAuR8IOAdAFD47HpCZRQ"></div>
		<asp:Button ID="Button1" runat="server" Text="Button" OnClick="Button1_Click" />
        <asp:Label ID="Label1" runat="server"></asp:Label>
</form>
</body>
</html>

[Load.aspx.cs]

CFFCS | CarrzSynEdit: | ASP.NET (VB/C#)

protected void Button1_Click(object sender, EventArgs e)
    {
        String strname = name.Text;
        String captcha = Request.Form["g-recaptcha-response"];
        //Next, we are going to make sure that each form variable has a value (Meaning: Filled out)
        if (strname == null || strname == "")
        {
            Label1.Text = "Please provide your name";
            //next, we are going to challenge the reCAPTCHA to make sure that it is not blank, 
            //and there is NO way around this. If it is not blank, then we send them a message.
        } 
        else if (captcha == null || captcha == "")
                {
            Label1.Text = "You have not completed the <strong>reCAPTCHA</strong>
Please click on the blank box.
Thanks You";
        }
        else
        { // If the user has completed the reCAPTCHA, then we send a message letting them know.;
            Label1.Text = "Thank you for trying out the 
<strong>ASP.NET (C# Version) / Jquery reCAPTCHA 2.0</strong> demo.";
        }
    }