That's already what we have now. Reuters stakes their credibility on this. They just don't have any.

> Spoofing the GPS

You can already do it now. Somebody even sells premade ones because some people what to screw up Pokemon go players. And it even already caused safety problems. It's the easiest thing of the whole part. Modifying camera require skills. Spoofing gps can be done with a gps spoofer that you may be able to buy somewhere.

If only GPS signals were cryptographically signed

Cryptographically signing GPS signals makes it harder to spoof GPS coordinates but does not stop it completely.

A spoofer could obtain signed GPS signals from the time and location where they are claiming to have taken a photo and combine them with a photo taken in a different time and place.

I was thinking that if secure timestamping could be done quickly enough, it might be possible to both bound the event by the future-light-cones of the spacetime points the GPS satellites sent the signed signal, and the past-light-cones of the timestamping event, but I suppose that’s probably not feasible (even with signed GPS signals).

Now, maybe on an interplanetary scale (with various sources playing the role of the GPS satellites, and various locations doing secure timestamping) it could be enough in order to be able to establish (beyond plausible hope of spoofing) a kind of rough region in space-time, but, maybe not very precise.