You're right, cameras can be tricked. As Descartes pointed out there's very little we can truly be sure of, besides that we ourselves exist. And I think deepfakes are going to be a pretty challenging development in being confident about lots of things.

I could imagine something like photographers with a news agency using cameras that generate cryptographically signed photos, to ward off claims that newsworthy events are fake. It would place a higher burden on naysayers, and it would also become a story in itself if it could be shown that a signed photo had been faked. It would become a cause for further investigation, it would threaten a news agency's reputation.

Going further I think one way we might trust people we aren't personally standing in front of would be a cryptographic circle of trust. I "sign" that I know and trust my close circle of friends and they all do the same. When someone posts something online, I could see "oh, this person is a second degree connection, that seems fairly likely to be true" vs "this is a really crazy story if true, but I have no second or third or fourth degree connections with them, needs further investigation."

I'm not saying any of this will happen, just it's potentially a way to deal with uncertainty from AI content.