Curious about the backgrounds

Does anyone know if all the still backgrounds (such as when cars were pulling up to the observatory) are matte paintings, or just still images being back-projected?
These backgrounds had such an unusual quality, I don't think I've ever seen a film that looked quite like this. I'm almost positive many of these were still images being back-projected, but I've never really seen this sort of use before (or perhaps, just haven't noticed it?), anybody know if that is what they were doing?

Zagreus waits at the end of the world, For Zagreus is the end of the world.