I understood the GP so that only some unique ID or hash of the original image would be included, not the image itself. Basically like the commit chain of Git but without the actual content blobs.

You could use this data to prove that image B is an edit of image A if you already have both A and B.

I still think this is a bad idea, because this all requires the images to have some sort of ID - and that seems like a prime target for tracking.

You can publish a fully stripped image (as people do now for exif), and retain the original