Hello,

Here is a tutorial to install the Captcha from Google (reCAPTCHA) in a BizForm for Kentico.


Sources :
- From Kentico Developer's guide.
- From reCAPTCHA developer's guide.


Tutorial :

1. Log in or sign in a Google account and get a public and private key for the reCAPTCHA webservice.

2. Open the web project in Visual Studio (or Visual Web Developer) using the WebProject.sln file or using File -> Open -> website in Visual Studio.

3. Right-click the CMSFormControls folder and choose Add New Item.
Choose to create a new Web User Control and call it recaptcha.ascx.

4. Add the following code in the recaptcha.ascx file :

<%@ Control Language="C#" AutoEventWireup="true" CodeFile="recaptcha.ascx.cs" Inherits="CMSFormControls_recaptcha" %>
<%@ Register TagPrefix="recaptcha" Namespace="Recaptcha" Assembly="Recaptcha" %>
<recaptcha:RecaptchaControl
    ID="recaptcha"
    runat="server"
    PublicKey="enter your public key here"
    PrivateKey="enter your private key here"
    Theme="red" 
    />

You can find all options on the reCAPTCHA developer's guide.

5. Switch to the code behind. Add the following code :

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
public partial class CMSFormControls_recaptcha : CMS.FormControls.FormEngineUserControl{
    protected void Page_Load(object sender, EventArgs e){
    }
    public override bool IsValid(){
        Page.Validate();
        if (Page.IsValid){
            return true;
        }
        else{
            return false;
        }
    }
}

6. Login to Kentico backoffice. Go to Site Manager -> Development -> Form controls and click New form control. Enter the following values:
- Control display name: Recaptcha
- Control code name: RecaptchaControl
- Control file name: ~/CMSFormControls/recaptcha.ascx
Check the boxes :
- Use control for text
- Show control in document types
- Show control in BizForms
and click OK.

7. Go to CMS Desk -> Tools -> BizForms:
Edit your form. Go to Fields tab and add a new tab:
- Column name: SecurityCode
- Show on public form: check
- Field caption: Security Code
- Field type: select "Recaptcha"
- Maximum length: 100
- Allow empty value: check
- Default value: (empty)
and click OK.


Tips:
As the Customizing the Look and Feel of reCAPTCHA page explains, you can customize the captcha.
I try to use the "custom" theme. But it seems to works only if you add Javascript to your CMSformControl.
See below:

<recaptcha:RecaptchaControl
    ID="recaptcha"
    runat="server"
    PublicKey="enter your public key here"
    PrivateKey="enter your private key here"
    Theme="custom" 
    />
<script type="text/javascript">
var RecaptchaOptions = {
   theme : 'custom',
   custom_theme_widget : 'recaptcha_widget',
   lang: '<%=CMSContext.CurrentDocument.DocumentCulture.Substring(0,2)%>'
  };
</script>

<div id="recaptcha_widget" style="display:none">
	Here you have to put all the captcha tags, as explain in the Customizing the Look and Feel of reCAPTCHA page.
</div>

Please note here the <%=CMSContext.CurrentDocument.DocumentCulture.Substring(0,2)%> get the current language (like "fr" or "en"). It can be usefull for multiple language web sites.