Signing the raw image data wouldn't require also signing the EXIF metadata. For privacy, you could later strip out everything except the raw image and the camera's signature and still prove that the image is unaltered.

Ontop of this, including a photo edit history in a photo including the original photo would increase the size of a photo to be completely unusable or unshareable.

In the contexts where you need to prove an image is a real unaltered photograph (court cases, news media, science, etc) privacy is usually not a concern.

Nobody cares if your social media photos are edited, they probably are, it's fine.

>EXIF data is stripped for a good reason - because it can be a privacy hazard. Suddenly this plays no role anymore?

Can you clarify what your actual complaint is here? Putting aside for a second obvious implementation options, it's pretty standard that there can be a tradeoff between privacy and trust. Any of us are still perfectly free to upload images for fun to forums or social media or whatever that are private, or edited or whatever we like. But if there's something we [i]want[/i] to prove, this gives an extra option to do so. And in particular the set of cases where one cares the most about enhancing authenticity appears at first thought to be pretty much a union set with the cases where one will put their name (or at least the location and time of the picture in question) behind the image? Like, can you give examples of specific cases you are imagining where simultaneously the photo itself reveals no information about time and location [i]and[/i] it's something local/national/international-newsworthy where people would fear AI-alteration? Like, say you're photographing at a protest to document it including any violations of law. By definition, the images you take reveal the location and the time. That's the whole point of them. Having the location and timestamp signed wouldn't reveal anything extra as long as the photo was unaltered.

And actual legit journalism always has name(s) standing behind the reporting. Or for that matter, even if we're merely talking something like a review of a product, is it actually wrong to put a name or pseudonym behind that review if you expect readers to give you much credence? I mean, you'd be free in terms of law and tech to not bother. But even long before the current growing AI-slop age a lot of us have been starting to treat anonymous reviews with a lot of skepticism, or discounting them entirely for some product classes, for good reason.

Even in terms of maintaining privacy, remember we already have "tools" for that which this in turn could further help. You could privately report a tip to a reporter at a media organization, and then they could report on that without revealing you but be able to say "we verified the signature of the raw image and sensor data" alongside normal follow up. Then it's their name, but having a stronger chain behind it could still be helpful in places.

Finally getting back to "implementation options", there's no technical reason the image and multiple sets of metadata can't all be signed separately by the sensor stack such that you can pick & choose what to include and still have it all be signed, with readers giving greater or lesser weight to the trust based on your choices.

https://www.da.vidbuchanan.co.uk/blog/android-c2pa.html

is a post about Google Pixel C2PA cameras experiencing contact with reality

Even if it's flawed, adding any friction at all to the effort of deception is a positive step.

The idea is to be able to prove that a photo you took was captured by a camera, not generated. That would be helpful in the context of a disputed news story, a court case, etc.

Would that ever be relevant for a screenshot?