I'm working on a script that will keep metadata in derivative files in sync with the master file or it's sidecars.
One of the mechanisms for this is to give a unique ID to the master file, either as an EXIF field or an IPTC field. I'm trying to avoid using the keyword field for this as in a million picture archive it would add a million keywords.
The obvious unique one is to join camara model-serial-shuttercount, but this is NOT generally preserved by a lot of programs, and not all cameras support this.
So I'm looking for a reference for what metadata is/is not preserved by major players in the image editing/image management arena. I'm hoping that someone has already consolidated this.
ImageMagick and exiftool seem to be able to pull whatever metadata exists from almost every image format out there.