If you want just to copy the IPTC data, eg. at the thumbnail creation, you don't have to parse the binary IPTC data into array and back; just do this:
<?php
$fullFilePath='photo1.jpg';
$fullPathThumb = 'photo1thumb.jpg';
$imagesize = getImageSize($fullFilePath, $info);
if(isset($info['APP13'])){
$content = iptcembed($info['APP13'], $fullPathThumb);
@unlink($fullPathThumb);
$fw = fopen($fullPathThumb, 'w');
fwrite($fw, $content);
fclose($fw);
}
?>