This is not a technical problem IMO. You can't cryptographically sign reality. There's always the analog hole
Reality has a pretty strong "hash" naturally built in. Even manipulated picture carries a huge amount of information that isn't changed or isn't changed as much as one thinks.
The manipulated pictures the motorcyclist uploaded still would give someone a good idea where and even when they were taken. That doesn't matter here but if you're making a more detailed argument, it's harder.
Just consider, "computer forensics" is a thing even though any single bit on the computer can be overwritten and "faked".
Reality has a pretty strong "hash" naturally built in. Even manipulated picture carries a huge amount of information that isn't changed or isn't changed as much as one thinks.
The manipulated pictures the motorcyclist uploaded still would give someone a good idea where and even when they were taken. That doesn't matter here but if you're making a more detailed argument, it's harder.
Just consider, "computer forensics" is a thing even though any single bit on the computer can be overwritten and "faked".