[someguyorother]

That seems to be a DRM problem. Let's say that you want the camera to track all modifications of the picture. Then, analogous to DRM, there's nothing stopping the forger from just replacing the CCD array on the camera with a wire connected to a computer running GIMP.

To patch the "digital hole", it would be necessary to make the camera tamperproof, or force GIMP to run under a trusted enclave that won't do transformations without a live internet connection, or create an untamperable watermark system to place the transform metadata in the picture itself.

These are all attempted solutions to the DRM problem. And since DRM doesn't work, nor would this, I don't think.

[chasil]

If a signed sha256 is somehow attached in the exif data, it can be removed.

What digital rights are there to manage? This would be a statement of authenticity, not proliferation control.

The vendor's private key would have to be stored in the device. How could it be protected from extraction?