2004.10.03 23:04 "Re: [Tiff] IPTC tags", by Bob Friesenhahn
I'm trying to work out how to read and write IPTC tags into TIFF images. I've downloaded the specification for IIMv4 from http://www.iptc.org/download/download.php?fn=IIMV4.1.pdf and I think that's fairly clear how an IPTC record is structured.
Also see contrib/iptcutil in the libtiff sources. Similar code may be found within GraphicsMagick (http://www.graphicsmagick.org/). GraphicsMagick includes a scrap of code (default disabled I think) for snarfing the IPTC record out of a Photoshop profile.