Cam: Some regular at audience-level aims a camera at the screen, usually with poor results. Easy to detect when the person in the next row gets up to go to the bathroom, if nothing else.

TS: "Telesync". Usually an inside job by a projectionist or similar, often with excellent audio (but sometimes not). Camera is usually very stable with an unoccluded view; these can be hard to detect if a viewer isn't paying particularly close attention.

Screener: Once upon a time, people with influence in things like the Academy Awards were sent physical copies of films to watch and judge a film at home. These copies were called screeners. Not as often a thing these days (with limited-access online streaming being a largely-solved problem), but they could be both very high-quality and very early. Sometimes, they included things like a periodic scroller or crawler that informed unaffiliated viewers that they were not allowed to be watching the thing they were watching. Sometimes, they also had one-off watermarks that were intended to show the source of a leak[1].

In the realm of leaky films, screeners were/are usually the superior format by a wide margin.

[1]: https://waxy.org/2014/01/ellen_degeneres_walter_mitty_screen...