I guess that during lockdown, people have more time on their hands to go through old photos, so I guess this is bound to happen.
Perhaps a workaround could be that the uploader of the photo adds a one line review to the pub giving a bit more info on when the photos were taken. Not ideal and no guarantee anyone would look at it, of course. But for pubs that don't attract a lot of reviews, it could be worth it.
I guess the other angle is that the dwarf approving the photo then has to realise it is a historical photo and suppress it in favour of more recent examples. For some photos I imagine it would be pretty obvious, especially if they date back decades, but for photos that are only 10 years old or so, it might not be obvious at first glance.