It was always impossible and you always had only two options - trust the person who told you, or see it so many times from so many original sources it's impossible to be fake. That's always been the case. I have seen fake wartime reports using photos from different conflicts, complete fabulations etc 20 years ago just as often as today - the good thing is that people finally recognize they shouldn't trust everyone and everything they see.
I'm sure a solution exists that can take inspiration from the digital rights people, anti-cheat developers, cryptography, and other industries interested in provenance.
Of course, nothing will be fool-proof, but perhaps something strong enough that social media websites require the uploaded media to have this provenance attestation as well.
But we're already there. The Gaza and Ukraine conflicts have been full of misinformation, especially showing pictures of attacks that either:
- were from that conflict, but not the particular attack that is being used to fuel upset reactions
- from other conflicts and labeled as being the current one