Using ReCaptcha in an MVC application

ReCaptcha.cs

// First, install the reCaptcha library from Nuget https://nuget.org/packages/recaptcha.
// Then, create your public and private keys at http://www.google.com/recaptcha.

// 1. Create an extension method to genereate the Recaptcha javascript
public static class Extension
{
	public static MvcHtmlString GenerateCaptcha(this HtmlHelper htmlHelper)
	{
		var html = Recaptcha.RecaptchaControlMvc.GenerateCaptcha(htmlHelper);
		return MvcHtmlString.Create(html);
	}
}

// 2. In the controller, add the CaptchaValidatorAttribute attribute and the captchaValid and captchaErrorMessage parameters to the method
[HttpPost]
[Recaptcha.RecaptchaControlMvc.CaptchaValidatorAttribute]
public ActionResult PostMessage(Message message, bool captchaValid, string captchaErrorMessage)
{
	if(captchaValid)
	{
		/// ... do something ... ///
	}
}

// 3. In the Global.asax's Application_Start method, assign you public and private keys
protected void Application_Start()
{
	Recaptcha.RecaptchaControlMvc.PublicKey = "0123456789";
	Recaptcha.RecaptchaControlMvc.PrivateKey = "9876543210";
}

// 4. In the view, add the following to generate the Recaptcha content
<tr>
	<td></td>
	<td>@Html.GenerateCaptcha()</td>
</tr>