[richardwhiuk]

It's basically impossible to tell, as a human, on YouTube which videos are sanctioned by Copyright owners and being monetized, and which are evading YouTube's Content ID systems. Clearly some are - e.g. videos where the content is horizontally flipped, or in a small box, or the audio is heavily distorted - but that's not universally true.

[thegeomaster]

You can usually click "Show more" in the video description and see if there's any copyrighted content identified by Content ID. If there is, most likely the copyright owners are getting the ad revenue (if it's not an official channel).

[baragiola]

I always assumed that VEVO were legal and the others illegal (unless uploaded by the artist, usually for amateurs or not-so-big-time artists)