I think both are good, it's nice to have variety. It was very satisfying as a user to think that the photo of all the people might be of the Egyptian revolution in 2011, then end up getting the year exactly right. Some photos are inherently gonna be easier to tell than others. Wartime photos can have a fun game of "figure out which war it is based on the equipment". I think the problem with the subway photo is that it's a very memorable situation, to use subway tunnels as shelters. But there are plenty of wartime photos that aren't gonna be that way.

I also like trying to figure out where the photo was taken, even if that isn't strictly part of the game. So I'm glad that the photo caption is there.