Generally, I think artwork is a tricky area because yes it's copyrighted and yes, if you take a photo of it there could be issues. My understanding is that if it's part of a bigger scene it's less of an issue, but I'm a bit grey on the details.

When I asked an art gallery permission to use some of my own pics in an editorial piece in a magazine they told me 'no' and sent me photos of theirs that I could use instead.

In terms of street art and murals, I struggle to imagine anyone suing someone, but maybe it depends on the use.

You're right to be cautious. I really should read up on it and perhaps write an article about what I find.

It's like logos and people, there can be issues with those as well, and sometimes, it depends on whether the place is public or private, whether they're a small part of a bigger scene, etc. And the final use of the image.

Unsplash notably doesn't cover artwork, logos, or recognisable people on their licence.