First of all, no "copy" (print) of a painting is EVER going to be worth even 1/10 of 1% of the original and that's because they're not painted by the original artist. They're machined (whether photo prints or canvas).
Let's try this again. A painting's value is based on it being the original. There are thousands of fakes Mona Lisa paintings out there, some painted by real people. But they're worth very little. Only the original is priceless. But since it's public domain (the image), it can be copied, imitated, cloned, whatever to your heart's content. But only the one painted by Da Vinci himself is worth the big money.
As I mentioned in my own response above, copying things for personal use at home (especially things you bought and want copies for the car, etc.) is a far cry from copying something and SELLING it (plagiarism and/or fraud in the case of original works of art as being the original made/painted by the original artist or pretending to be the original artist). In the case of music, software, etc. (digital stuff being copied and then sold) it's typically called "piracy". If you're not selling it, "piracy" really doesn't fit (it's possibly a copyright violation depending on the exact use), but the news/media likes to throw the word piracy around for everything these days.