An elderly couple in heavy coats are looking at black and white photos displayed on a wall.
Octogenarians admiring the old photographs that decorated th wall.
An elderly couple in their eighties would be octogenarians and old photos are frequently printed on black and white paper, so the second sentence is more descriptive about the elderly couples age as well as the age of the photographs.
An elderly couple can be Octogenarians, and old photographs are usually black and white photos.
Black and white photos are old photographs.