proving video plagiarism with compression artifacts

[NiHaoMike]

How difficult (or even possible) would it be to prove that video B that looks identical to video A is in fact a plagiarized copy of A that has since been reencoded? (And not vice versa.) My understanding is that A would have the compression artifacts from its encoding process, while B would have compression artifacts from its own encoding as well as compression artifacts of A that didn't get masked.
I'm aware that there are "watermarking" algorithms specifically designed for that, my question is if the original compression artifacts can act as that watermark.

[Haenk]

I'd say that will work, in general.
However consider "AI enhancing" (or other enhancing), which might unblur, sharpen, add details (that might or might not be there in the first place), but I'm sure, with a bit of experience, one could identify this as well.
I remember my first DVD-player, using an upscaler ASIC from Faroudja, which essentially does the mentioned picture enhancing and re-encoding. Amazing, but certainly detectable, if you know, what to look for...