2004.12.07 02:08 "Re: [Tiff] Having problems adding IPTC to a TIFF", by Bob Friesenhahn
I have communicated with Bill Radcliffe, the one who wrote the IPTC utility distributed with libtiff, and the author of the TIFF IPTC support in ImageMagick/GraphicsMagick and he believes that libtiff is correct in using TIFF_LONG. Given that he has been working in this area for many years, I am strongly inclined to trust his opinion on this.
ImageMagick/GraphicsMagick include byte-swapping code to deal with IPTC coded in both big and little-endian forms. The endinness is expected to match that of the TIFF file (based on TIFFIsByteSwapped()).