在表单中添加CAPTCHA

I am now using dform plugin for form creation. Creating normal fields work fine. Is there any plugin available for dform that contains CAPTCHA? Creating dforms require just json file and script file. How can we add CAPTCHA to it? I am using PHP as server side scripting language.

Recaptcha is a plugin that can be used with any form

Can be found here http://www.google.com/recaptcha

Here's example code on how to set it up http://code.google.com/p/recaptcha/wiki/HowToSetUpRecaptcha

<script type="text/javascript"
   src="https://www.google.com/recaptcha/api/challenge?k=YOUR_PUBLIC_KEY"
 </script>
 <noscript>
   <iframe src="https://www.google.com/recaptcha/api/noscript?k=YOUR_PUBLIC_KEY"
       height="300" width="500" frameborder="0"></iframe><br>
 </noscript>


 require_once('recaptchalib.php');
  $publickey = "YOUR_PUBLIC_KEY"; // You got this from the signup page.
  echo recaptcha_get_html($publickey);
With the code, your form might look something like this:

<!-- your HTML content -->
 <form method="post" action="verify.php">
   <?php
     require_once('recaptchalib.php');
     $publickey = "YOUR_PUBLIC_KEY"; // you got this from the signup page
     echo recaptcha_get_html($publickey);
   ?>
   <input type="submit" />
 </form><br>
<!-- more of your HTML content -->