Simple php function that writes IPTC data in a JPG image.

iptc.php

<?php
/*
Simple php function that writes IPTC data in a JPG image.
Details here: https://www.iptc.org/std/photometadata/specification/IPTC-PhotoMetadata
https://www.php.net/manual/en/function.iptcembed.php
*/

 function write_iptc($rec, $data, $value)
    {
        $length = strlen($value);
        $retval = chr(0x1C) . chr($rec) . chr($data);

        if($length < 0x8000)
        {
            $retval .= chr($length >> 8) .  chr($length & 0xFF);
        }
        else
        {
            $retval .= chr(0x80) .
                chr(0x04) .
                chr(($length >> 24) & 0xFF) .
                chr(($length >> 16) & 0xFF) .
                chr(($length >> 8) & 0xFF) .
                chr($length & 0xFF);
        }

        return $retval . $value;
    }

?>