I think it’s worth noting that even if the photo is CC0 licensed, users are still taking a risk by using the photo on their website if the photo was:

uploaded by someone else other than the copyright holder
contains an identifiable person who has not signed a model release
Was take on/of property that requires a property release.

Those are the filters I want to see added to WordPress Photos asap.

Unsplash also ran into this problem with some very high profile “misuses” due to these issues. I really hope WordPress Photos doesn’t make the same mistake.