Thank you for stating clearly situation. I fully agree with your assessment. For almost 10 years now I have been saying that we need to virtually watermark reality. By "virtual" I mean store the metadata about the digital capture on a public blockchain. Then my devices could have a built-in "fake vs real" detector.
Artists, photographers, journalist, etc. are going to want and need this.
Some sort of signatures to verify legitimate unmodified photographs (taken with a relatively secure device, e.g an iPhone) seems like a reasonable idea
But even then, people will be able to point that camera at a manipulated/generated image (either printed or on a screen). Maybe that one could be solved if the photo included some depth information?
a lot of cameras do have an in camera hardware based cryptographic signing (i think it runs off its own chip on them?) but any modifications to the image immediately break that. so for stuff like journalism etc where youd hopefully have a lot of settings dialed in on camera for quick turn around would keep that fingerprint intact.
Editing is fine as long as you keep the signed original for validation purposes.