It suddenly occurs to me that I copied a database photo into a thread posting without asking permission from the photographer. I've read lots of postings with similar DB photos, and used one myself without thinking. Should I have approached the contributor of the photo?

Photos in ATP database can be use on ATP thread post without contacting the person who contributed it to the database.
As a matter of fact I think it is encourage because it helps draw attention to the database.

I highlight and copy/paste the ATP photo bb code or whatever it's called from photos in the database all the time to put on threads I'm chatting on ... like your beautiful database photo below.

both - that's a relief!