Oops duh I think I just stumbled on how to do it. It's the DB code associated with each picture in the database, right? Doh!
Except that while this shows a particular database picture (and who posted the picture), it links ONLY to that picture, and not to the plant's database entry itself. So I still need some help there... (unless there is a separate db_x tag that links to the database entry, and one particular photo is always fixed to that).
Off to check!