I am not new to photography, but this seems to be such a basic question so I am posting it here. (maybe it is not so basic since I never thought about it until now )

What exactly is the publication date for a photograph? When the negative is processed? When the shutter is pressed? When the first print is made? When it is posted online? Used in advertisement? etc I am guessing the real answer may be complex due to new technology and old laws.

This is specific to copyrighting photographs.

I am organizing some of my old negatives that I didn't like so much when I first took them, but now with the filter of time, they are looking pretty good to me. I am planning to register the copyright, but don't know how to sort them by year for a "group".

Thanks in advance for any input!

If you're in the U.S., take a look at the FAQ item What is publication? and Copyright Office Basics: Publication.

As far as I am concerned, it is published when I post it on my website. Since I license only through my website, any image that is used ("published") by someone else has been first published on my website. That provides me with a simple means to know the date of first publication that I use for registration.