<?php
declare(strict_types=1);

$image = imagecreatetruecolor(8, 6);
imagejpeg($image, "photo.jpg");
$caption = "Manual photo";
$block = chr(0x1c) . chr(2) . chr(120) . pack("n", strlen($caption)) . $caption;
ob_start();
$ok = iptcembed($block, "photo.jpg", 2);
$bytes = ob_get_clean();
echo $ok && strlen($bytes) > 0 ? "JPEG output captured\n" : "failed\n";