There are a few different kinds of 'secure enclaves' implemented on chips, where you can have some degree of trust that it "cannot" be faked.

E.g. crypto wallets, hardware signing tokens, etc.

We could imagine an imaging sensor chip made by a big-name company whose reputation matters, where the imaging sensor chip does the signing itself.

So, Sony or Texas Instruments or Canon start manufacturing a CCD chip that crypto signs its output. And this chip "can't" be messed with in the same way that other crypto-signing hardware "can't" be messed with.

That doesn't seem too far-fetched to me.

* edit: As I think about it, I think more likely what happens is that e.g. Apple starts promising that any "iPhoneReality(tm)" image, which is digitally signed in a certain way, cannot have been faked and was certainly taken by the hardware that it 'promises' to be (e.g. the iPhone 25).

Regardless of how they implement it at the hardware level to maintain this guarantee, it is going to be a major target for security researchers to create fake images that carry the signature.

So, we will have some level of trust that the signature "works", because it is always being attacked by security researchers. Just like our crypto methods work today. There will be a cat-and-mouse game between manufacturers and researchers/hackers, and we'll probably know years in advance when a particular implementation is becoming "shaky".

How would such a camera ensure you're not taking a picture of a picture?

Just get a really really nice screen to display deepfakes on before photographing them

Maybe have the signed content include a timestamp and location? But... GPS can be spoofed I think.

In which case if found out will result in that person / publishers credibility going down the drain.

We will learn to trust sources (cryptographically signed) rather than just what we see.

Maybe at some point for some cameras. But not soon after their release if they took steps to protect their pipeline with hardware.