That's just a timestamping service then, not a content provenance/authentication scheme. Timestamping has been a solved problem for years; certificate authoriti

That's just a timestamping service then, not a content provenance/authentication scheme. Timestamping has been a solved problem for years; certificate authorities offer this, or you could just throw a hash onto any sufficiently trusted blockchain. Nothing prevents anyone from opportunistically pre-generating and timestamping millions of permutations of fake kompromat and then selectively revealing the one that turns out to be useful after the fact. You could charge per attestation, but the economics of that don't look great; you could demand publication of the image itself before attestation, but that would obviously not fly for most use cases out of privacy concerns.