In regards to your question about hidden methods to catch people, back before digital each film print sent to a theater had a unique “CAP Code” printed directly onto the 35mm film. This was a series of dots in a unique pattern that would show up several times on screen. So when a cam rip would show up somewhere this could be used to narrow down which theater it was recorded at and identify trends after several films.
I don’t know if this was ever successfully used to prosecute anyone though.
I disagree, the vast majority just need a browser, your use case may be quite common, but definitely not the majority.