You might have noticed that several metadata fields in Photoshop are not available via IPTC.
I have written a library "PHP JPEG Metadata Toolkit" which fixes this problem as it allows reading, writing and interpreting of virtually any type of metadata, including these missing fields.
Try it out, and download it at:
http://www.ozhiker.com/electronics/pjmt/index.html