PHP

php recaptcha

<?php
  if(!empty($_POST['g-recaptcha-response']))
  {
        $secret = 'GOOGLE_CAPTACH_SECRET_KEY';
        $verifyResponse = file_get_contents('https://www.google.com/recaptcha/api/siteverify?secret='.$secret.'&response='.$_POST['g-recaptcha-response']);
        $responseData = json_decode($verifyResponse);
        if($responseData->success)
            $message = "g-recaptcha varified successfully";
        else
            $message = "Some error in vrifying g-recaptcha";
       echo $message;
   }
?>

php recapcha

<script src='https://www.google.com/recaptcha/api.js' async defer ></script>