reCAPTCHA

Google has improvement it's captcha and introduced new reCAPTCHA

reCAPTCHA

 

Follow below steps to implement reCAPTCHA:

1- Sign up google reCAPTCHA site:
http://www.google.com/recaptcha/intro/index.html

2- Register your site domain. after thar it will give you "site key" and "secret key"

ON CLIENT SITE:

1- Paste this line in your web page.
<script src='https://www.google.com/recaptcha/api.js'></script>

2- Paste the <div> tag as same in reCaptcha site:
<div class="g-recaptcha" data-sitekey="YOUR-SITE-KEY"></div> 

ON SERVER SITE:

1-  Send three variable as POST method to url  
https://www.google.com/recaptcha/api/siteverify

Post variable are: secret, response, remoteip
where secret is the your Secret Key
response is recaptcha
remoteip is your remote ip address

//CHECK reCAPTCHA in PHP code
$g_r_r=$POST['g-recaptcha-response'];
if(!empty($g_r_r) && strlen($g_r_r)>0) { 
  $gurl="https://www.google.com/recaptcha/api/siteverify";
  $scrt='YOUR-SECRET KEY';
  $my_ip=$_SERVER['REMOTE_ADDR'];
  $url=$gurl."?secret=".$scrt."&response=".$g_r_r."&remoteip=".$my_ip;
  
  $c = curl_init();
  curl_setopt($c, CURLOPT_URL, $url);
  curl_setopt($c, CURLOPT_RETURNTRANSFER, 1);
  curl_setopt($c, CURLOPT_TIMEOUT, 30);
  curl_setopt($c, CURLOPT_USERAGENT, "Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US; rv:1.9.2.16) Gecko/20110319 Firefox/3.6.16");
  $c_data = curl_exec($c);
  curl_close($c);
  $res= json_decode($c_data , true);
  if($res['success']>=1) {
    //IMPLEMENT HERE LOGIN LOGIC OR ANY OTHER LOGIC
  }
}