I wonder whether Twitter users are really legally liable for copyright violation in tweets they retweet, or whether the enforcers just believe they can get away with it.
I suppose it might differ from one jurisdiction to another. Are enforcers of this kind usually in the same jurisdiction as the supposed infringer?
However, doesn't Twitter itself add images in some cases (especially where a user tweet a link, but probably also retweets of an image)? If Twitter still does that, does it suggest Twitter itself isn't being targeted for enforcement? If so, is that only because enforcers prefer smaller prey?
Anyway, best of luck to you and your wife!
If the users are sufficiently anonymised, or share accounts, prosecution might be difficult, but I'm not sure that makes them any less liable. I don't imagine that accounts themselves could be prosecuted, but I'm not a lawyer.