check_recaptcha.php

<?php
function checkRecaptcha($recaptcha_response){
    $url = 'https://www.google.com/recaptcha/api/siteverify';
    
    $fields = array(
        'secret'    => 'YOUR_SECRET_KEY',
        'response'  => $recaptcha_response,
    );
    
    $fields_string = '';
    
    foreach($fields as $key => $value) {
        $fields_string .= $key.'='.$value.'&';
    }
    
    rtrim($fields_string, '&');
    
    $ch = curl_init();
    
    curl_setopt($ch,CURLOPT_RETURNTRANSFER, 1); 
    curl_setopt($ch,CURLOPT_URL, $url);
    curl_setopt($ch,CURLOPT_POST, count($fields));
    curl_setopt($ch,CURLOPT_POSTFIELDS, $fields_string);
    
    //execute post
    $recaptcha_query = json_decode(curl_exec($ch), true);
    
    //close connection
    curl_close($ch);
    
    return ($recaptcha_query['success'] == 1);
}
?>