Is it illegal to print and sell paintings and calligraphy downloaded from the Internet?

It is illegal and infringing. If the original author is alive, according to international copyright, printing, selling or trading without the authorization of the original author is regarded as infringement.

However, if the original author died more than 50 years ago and there is no heir to the copyright law, it is not illegal and can be marked as printed matter when selling.

But my personal opinion, then again, if it is printed for sale, it should be marked as printed matter. If the price is not expensive, no one will report it. Even if the original author knows that most people won't say anything, the overall meaning is that no one will report it and nothing will happen. But this is an infringement. Someone must have something to report.