That has changed recently, people in these communities believe that NFTs are only valid if verified by opensea. So you are now buying ownership as opensea is beginning the enforcement of copyright.
Opensea might be verifying the rights owner has attached their image to an NFT, but that still doesn't mean they have transferred any rights to the holder of the token. Correct me if I'm wrong I've not looked up Opensea's T&C's (have several other's).
Also whenever people talk about ownership in regards to copyright, it's a flag that they probably don't know what they are talking about.
For most of these people the NFT is the valuable part. If Twitter verifies your opensea nft and let's you put it on your Twitter profile that is the value.
Technically violations are determined by a court. If no one has accused you of a violation and no court has found you in violation then you are not in violation.
A separate question is would the copyright holder win a lawsuit or DMCA takedown request? I don't know
They are pulling a bait and switch.