This took me longer than it ought to to figure out. Very handy for handling a stream of photos where the info you want is in the IPTC header. This example passes by reference, for which PHP4 will yell at you. If your need to write into the header, check out the Image::IPTCInfo Perl module.
$size = GetImageSize ("$image_name",&$info);
$iptc = iptcparse ($info["APP13"]);
if (isset($info["APP13"])) {
$iptc = iptcparse($info["APP13"]){
if (is_array($iptc)) {
$caption = $iptc["2#120"][0];
$graphic_name = $iptc["2#005"][0];
$urgency = $iptc["2#010"][0];
$category = $iptc["2#015"][0];
// note that sometimes supp_categories contans multiple entries
$supp_categories = $iptc["2#020"][0];
$spec_instr = $iptc["2#040"][0];
$creation_date = $iptc["2#055"][0];
$photog = $iptc["2#080"][0];
$credit_byline_title = $iptc["2#085"][0];
$city = $iptc["2#090"][0];
$state = $iptc["2#095"][0];
$country = $iptc["2#101"][0];
$otr = $iptc["2#103"][0];
$headline = $iptc["2#105"][0];
$source = $iptc["2#110"][0];
$photo_source = $iptc["2#115"][0];
$caption = $iptc["2#120"][0]; }}
