Keys could be stored in something like TPM on Camera, and could sign the image. The key could then be verified from the camera itself to prove the authenticity of the image.

If we as a society deemed it necessary, the camera manufacturer could also provide a list of keys for devices they have manufactured. And an image/key could be provided, and the manufacturer could verify the authenticity that way.

The TPM signing could be tied into the sensor hardware itself, making it difficult, but not impossible, to sign arbitrary images with the TPM.

Some ways someone might break this particular system:

If the TPM signs the original image taken by the camera, then even the slightest image processing on another device would invalidate the signature. Routine changes like cropping, scaling, converting between image formats / quality levels, or applying image filters would invalidate the signature.

It's also surely hard to prove when a picture was taken, because an adversary could manipulate the date/time settings on the camera and forge evidence to frame someone. "This cryptographically signed photo, with timestamp, proves that you were here at this time!"

And camera sensors can get damaged and need replacement. If the TPM and sensor are tightly coupled, that would mean they both have to be replaced. But if replacement is allowed, then you can just as well replace the TPM+sensor with a sensor from another camera. In which case a signature from a specific TPM-sensor doesn't prove that a specific camera took the photo, at best it might be evidence that a specific camera model took the photo.

If you can replace a sensor without replacing the corresponding TPM, then someone can create a fake sensor module that feeds the TPM with arbitrary data, which it will happily sign thinking it's a real image. So someone can sign an image with a fake sensor, then restore the original sensor and claim that an arbitrary picture was taken with that camera.

So let's just say TPM+sensor must be replaced together. Maybe only the manufacturer can create the TPM+sensor, so they would be the source of this replacement part. But if the manufacturer will happily ship a replacement TPM+sensor for a specific camera, someone can fraudulently claim that their sensor is broken and be given a new TPM+sensor for the same camera. And there will now be multiple TPM+sensors in existence that have the same key. Since this module can be switched between cameras, there could be multiple cameras that signed a given picture.

Finally maybe the manufacturer doesn't want to deal with the above problems and decides that repairing the camera's TPM is not allowed after all, but then they will be in violation of right-to-repair laws in several jurisdictions.

If I steal your camera while you're on vacation, do I then gain proof of ownership of your photos?

If I need to reset TPM, how do I reclaim photos I took previously?