Lots of industries/companies are required law to maintain records of what they do. If such requirements were imposed on media companies, it could be done by archiving source material and using nondestructive editing software that saves edit decision lists.

Laws requiring media production companies to keep these records seem implausible in America, but at least conceivable in some of countries.

That's why I specifically mentioned the structure of the image. You'd still have to differentiate lens corrections, but structural changes could be counted differently from color / sharpening corrections / standard postprocessing.