I'd like to use a Henry Fuseli's "The Nightmare" as an album cover of mine. May I? Or who should I speak to about it?

Just try information desk.

That's a long and sometimes confusing road you'll need to contact the museum depending on what type of album check copy right laws too to protect yourself

The information desk can answer your question if not they can point you in the right direction

Call information desk for details.

I would call their information number and ask someone. G