[justinpombrio]

The painting itself. But the right to reproduce the painting is covered by copyright, and ends up in the public domain 70 years after the painter's death, same as everything else. (Such a long time! It was originally 14 years with an optional 14 year extension period.)

https://www.arsny.com/copyright-basics/

So a (freelance) painter gets two things: the physical piece of art, and the right to reproduce it. A musician can get concert revenue, plus the rights to reproduce their music. I don't have a good sense about how the values of these things compare.