if (class_exists('\CURLFile')) {
    $field = array('fieldname' => new \CURLFile(realpath($filepath)));
curl_setopt($ch, CURLOPT_SAFE_UPLOAD, true);
} else {
    $field = array('fieldname' => '@' . realpath($filepath));
curl_setopt($ch, CURLOPT_SAFE_UPLOAD, false);
}