I recently wrote a program to view my pictures and edit the jpeg metadata. The idea is that it would be a nice interface for browsing pictures and metadata and allow quick changes to the comments field. Vista provides this support (It’s fantastic!) but I’m still running on XP on my main machine. My pictures are taken from my new Palm Treo 700wx, which has a nice quality camera, but fails to properly white-balance most photos (although in its defense, most cheap digital cameras don’t have good white balance). As a result, I was using the gimp to alter the levels of the image. However, it seems that gimp decides, when it is saving the file, that it will completely throw out metadata. This doesn’t completely surprise me, but is quite annoying, since it means that once you have metadata in a jpeg file, it is quite difficult to edit the data and preserve the metadata. This would require additional support from gimp, but it isn’t like jpeg is the only format that supports property tags. Off the top of my head, I know that Tiff files support some sort of properties, and I’m sure other files have a feature similar to ID3/EXIF type metadata.
I’m kind of curious if Photoshop preserves metadata. I would assume it has some sort of support for this, considering that it is the most commonly used photo editing software by professionals.