Copyright holders already have legal processes to follow: DMCA takedown notices (sent under penalty of perjury) and civil lawsuits. If they don't choose to use them, tough.
They frequently bleat that it's expensive. It is, but mainly for the people they accuse, who can't afford to defend it.
They frequently bleat that it's difficult to prove. That's hardly an excuse to make accusation the only burden of proof required, is it?