Ok, let's apply this logic to the other arts.
The piano teacher down the road uses pop songs to help teach his students how to play the instrument. You want to forget what the law allows and have him contact Elton John for permission every time he shows a kid the melody to Tiny Dancer?
Before an acting coach has a student learn a monologue from Our Town, she has to get permission from the estate of Thornton Wilder?
That's not how things work. That's not how they're even required to work.
I understand where you're coming from, but she could switch out your painting for another, and it changes nothing. The money she makes doesn't come from your painting, it comes from the instruction. As I said before, just be happy for the free advertising and ignore the people encouraging you to get into a fight.
And that was an interesting point about respect. I think it points to the fact that a lot of these issues have less to do with legal issues and more to do with emotion, which would explain why illogical positions are defended so vigorously.