// At the top of generate_pkpass.php
define('PASS_IMAGES_DIR', '/full/path/returned/by/fix_images.php/');

// When adding images
$images = [
    'icon' => PASS_IMAGES_DIR . 'icon.png',
    'logo' => PASS_IMAGES_DIR . 'logo.png'
];

foreach ($images as $key => $path) {
    if (file_exists($path)) {
        $pass->addFile($path, $key . '.png');
    }
}