... and that is fine as long you let people know that it not an original van Gogh.
Unfortunately, you picked a bad example: a painting is a finite resource -- there is only one physical painting painted by the original artist. A painting cannot be "copied" with the same veracity as software can be (bitwise, which in the case of software becomes piracy) and any attempt to pass a "copy" of a painting as an original is forgery.
Classifying any work (art/software) as a rip-off requires defining the very fine line between fair-use and unfair forgery. When it comes to artistic endeavors (as in "design"), you'll have more luck defining the position and velocity of an electron around a nucleus than delineating that fair/unfair boundary.
Unfortunately, you picked a bad example: a painting is a finite resource -- there is only one physical painting painted by the original artist. A painting cannot be "copied" with the same veracity as software can be (bitwise, which in the case of software becomes piracy) and any attempt to pass a "copy" of a painting as an original is forgery.
Classifying any work (art/software) as a rip-off requires defining the very fine line between fair-use and unfair forgery. When it comes to artistic endeavors (as in "design"), you'll have more luck defining the position and velocity of an electron around a nucleus than delineating that fair/unfair boundary.