Wow, been a long time since I've heard that term used towards photos. So long, I had to go and look it up
I found this information on it here
, which you might already know.
I also found this page here
which will allow you to download a program to read/write metadata to pictures.
The above may or may not be what you're looking for. I think that the 2nd link will be of more use to you, assuming that the program does what you need it to.
If you're using Photoshop, you can do pretty much the same thing from within photoshop by going to File>File info (or Alt+Ctrl+I). This will allow you to input all sorts of (all text) data about the photo or anything else you want. I've used this for years, as it allows users to view info from/about the image right from photoshop itself, so they don't have to open another program to pull metadata from an image.
Other freeware apps (photo editing ones) may or may not allow you to do the same (File>file info).
Hope this helps. If not, post back and someone else might be able to help you out.
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