You might have noticed that several metadata fields in Photoshop are not available via IPTC.
Also, Photoshop now uses XMP for it's primary metadata, meaning IPTC is only read by Photoshop if XMP is not present.
I have written a library "PHP JPEG Metadata Toolkit" which bypasses this problem as it allows reading, writing and interpreting of virtually any type of metadata, including XMP, IPTC and EXIF.
Try it out, and download it at:
http://www.ozhiker.com/electronics/pjmt/index.html