Get secure thumbnail from Wordpress

secure.php

function the_secure_post_thumbnail($size, $options) {
  ob_start();
  the_post_thumbnail($size, $options);
  $thumbnail = ob_get_clean();
  $secure_thumbnail = make_secure($thumbnail);
  echo $secure_thumbnail;
}

function make_secure($url) {
  $secure_url = $url;
  if(is_ssl()) {
    $secure_url = str_replace('http', 'https', $secure_url);
  }
    return $secure_url;
  }
}