Sure, I was thinking about a photo of human subjects in the foreground, with some distant buildings in the background. But if you photograph the shadow of the Eiffel tower on a clear sunny day you may be down to the precision of a couple of minutes.

But that's only if you can resolve the "which day" issue?

Oh, yes, that seems a hard problem. But with sufficient effort (cloud patterns, parked cars, other people in the image) there is still a lot of information to extract. Especially if other people were taking exim-tagged photos in the same time and place and putting them on instagram.