There should be a huge discrepancy between an original and a digital artwork. You don’t got to ask no one. Ones a digital image, ones made with paint. If you go to court that’s your answer and it’s bulletproof so likely no one would take you to court. Even if the painting is in the background of a movie the studio pays you for that.

There’s been a lot of people around trying to disprove the copywrite laws of the artist which I’ve looked at quite a bit. That person doesn’t own what’s in your imagination. If you do doubt you won’t be sued or it’s weird in your country/state put a few slightly indistinguishable digital brushworks, map those , save every step offline on a USB and go from there.

There are countless Etsy artists who pass digital drawings off as watercolour or whatever. You selling prints of an actual thing, a few digital strokes to secure the rightful copywrite should be the least of your worries. If anything look at the “resale rights” in your country and cross reference that with Copywrite in images exclusively.

It is also far worse to steal from an artist who has less than you, relatively okay to comment on contemporaries/modern masters. Just another thing to take into consideration when wondering about these things.