I think it’s reasonable to assume that because something is labeled CC-BY that it’s legal to use for situations allowed by CC-BY.
Is there some copyright certification service? Is there a way to test copyrights? If I don’t go my the author’s copyright, how could I verify it?
If I watch a movie, should I not do so until I verify the personality rights of every person who appears in the film? How can I trust Disney?
edit: As for your example, copyright generally doesn't care about you consuming a work but about you sharing a work. As such, you don't have to check anything but Disney does have to check everything.
Disney, and random youtuber, does have to check everything, not me if I’m legally using it. However, if the copyright if wrong, I’m not sure what the liability is.
The way that publishers, for example, avoid such pitfalls is by exclusively working with professional agencies that control the provenance of the work they license.
Watching anything isn’t copying nor showing and therefore safe. Practically, if you want to use any CC-licensed photos, I would advise at least a reverse image search.
I suspect that even in the US there is more to it. For example, stock photo agencies treat copyright and model releases as separate things. For any non-editorial images that contain recognizable faces they are in my experience strict about about getting a proper model release.