reCAPTCHA is a free CAPTCHA service that protects your site against spam, malicious registrations and other forms of attacks where computers try to disguise themselves as a human;

A CAPTCHA is a Completely Automated Public Turing test to tell Computers and Human Apart. reCAPTCHA comes in the form of a widget that you can easily add to your blog, forum, registration form, etc. Therefore, reCAPTCHA has been become the most powerful captcha to prevent against SPAM or automatic form filling script attacks.

To learn how reCAPTCHA works, read it here. There are a PHP plugin for reCAPTCHA which you can download it here and if you would like to read it's documentation, you may read it here.

If you had already running a web application (most likely a website or blog) based on Panada Framework. I had the PHP plugin conversion for Panada Framework library for you to use. You may download the reCAPTCHA library here:

• Initial release
  reCAPTCHA Panada Framework library v1.0 (9.79 kB)  - download 
  Notes: This library conversion was built based on reCAPTCHA PHP plugin v1.11

Installation

Follow these steps to install and use the library on your Panada application:

1. Put the downloaded library file on your apps/library/ folder, so it has the following path:
   /apps/library/recaptcha.php where / is your Panada application root directory.
2. Create your own reCAPTCHA API key here to get your reCAPTCHA public key and private key.
3. So now you already have your public key and private key.
   Put your public key and private key on your panada application configuration file: /apps/config.php
   Add the following lines to your configuration file:
   
   
   /* reCAPTCHA key configuration */
   $CONFIG['recaptcha_publickey'] = "your_public_key";
   $CONFIG['recaptcha_privatekey'] = "your_private_key";
   
   replace your_public_key with your already created reCAPTCHA public key and replace your_private_key with your reCAPTCHA private key

<?php

    $recaptcha = new library_recaptcha();
    echo $recaptcha->recaptcha_get_html($this->config->recaptcha_publickey); 

?>

// ... your previous php code ...

$recaptcha = new library_recaptcha;
$resp = $recaptcha->recaptcha_check_answer ($this->config->recaptcha_privatekey,
    $_SERVER["REMOTE_ADDR"],
    $_POST["recaptcha_challenge_field"],
    $_POST["recaptcha_response_field"]);

if (!$resp->is_valid) {

    // What happens when the CAPTCHA was entered incorrectly
    die( "The reCAPTCHA wasn't entered correctly. Go back and try it again." . 
    "(reCAPTCHA said: " . $resp->error . ")" );

} 

// ... your next php code ...