In the US, copyright status is determined by when something was published, not how old it is. The two are not related. That's how we get stupid things like the University of California and the Mark Twain Foundation claiming a copyright on his autobiography, written circa 1909, until 2047 - 137 years after his death.[1]
So if I found an amateur painting that was centuries old in an attic somewhere, and posted a scan of it on my blog, I would then be the copyright holder of that painting? That feels so wrong.
My understanding of copyright rulings in the US (eg see Bridgeman Art Library v. Corel Corp. above) is that a faithful photograph of a painting is not considered "original". Therefore, if I do not have the copyright to the painting, neither would I have copyright over the photo.
[1] https://en.wikipedia.org/wiki/Autobiography_of_Mark_Twain#Ma...