ct.php

$recaptcha = $_POST['g-recaptcha-response'];
$res = reCaptcha($recaptcha);
if(!$res['success']){
  // Error
}
function reCaptcha($recaptcha){
  $secret = "6LeBBdwZAAAAAJWmaS22gjjx6Nznn7KGyJudKSTA";
  $ip = $_SERVER['REMOTE_ADDR'];

  $postvars = array("secret"=>$secret, "response"=>$recaptcha, "remoteip"=>$ip);
  $url = "https://www.google.com/recaptcha/api/siteverify";
  $ch = curl_init();
  curl_setopt($ch, CURLOPT_URL, $url);
  curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
  curl_setopt($ch, CURLOPT_TIMEOUT, 10);
  curl_setopt($ch, CURLOPT_POSTFIELDS, $postvars);
  $data = curl_exec($ch);
  curl_close($ch);

  return json_decode($data, true);
}