WAIT a minute! If the painting is original, it's original and NOT copied. A copyist cannot claim "originality". However, if its a painted copy or facsimile of an original, the copyist must credit the original artist - even if its a photographer. I know, because I sometimes use photos for my own "art models" - not having any live models at hand. However, I am not a copiest nor a duplicator. I use a figure or face in a photograph as a guide for proportion and gesture for my entirely original subject.
Outside of academic settings, is there any requirement to credit public domain works? To be sure, it's generally done, but if I paint a woman who looks like the Mona Lisa standing next to Abraham Lincoln, do I have to credit either Leonardo da Vinci or the original photographer?
Well, thanks for that hypothetical! What I can tell you is this: some of my artist friends who copy/trace/photo project paintings, reproductions (prints,) illustrations or photographs, or parts thereof, must credit the originator IF the painting is offered for sale or exhibited.
As an example, my artist colleague copied (painted) a (millpond) scene from an old battered oil painting by an obscure artist. Because she planned to exhibit her painting for sale, she felt ethically obligated to credit the artist by noting on the back of her painting, "Based on a oil painting dated 1921 by John Doe." Her rendition slightly resembled the original because she changed the light source, the figure's clothing colour and the foliage around the pond, some background slightly different. Whether or not artist John Doe had a copyright, this is the ethical thing to do.
Ward Churchill's plagiarism and fraudulent representation is blatant, absolutely blatant!
It's certainly is a condemning load of S**T pouring out of Churchill's closet. I find that very consoling.
Certainly it would generally seem ethical, but I've seen plenty of works that were obviously derived from da Vinci or other artists with no overt credit given. Further, in things like movie scores, it's quite common to hear snippets of public domain tunes with no credit given to them (sometimes public domain works are credited, but not always).
To be sure, one must invest a certain level of creativity in a work derived from a public domain work before one can copyright it. I would guess some of Churchill's serigraphs probably meet this criterion as general works of arts, though art prints have some special rules if they are to qualify for certain special copyright protections.
BTW, another thing I was curious about: suppose I buy at an estate sale a camera positive (reversal film) movie made after 1948. What would the copyright status of the film be? I would think that, in the absense of any documentation to the contrary, buying the original film would give me the copyright to it. But what are the actual rules?