Comment by WalterBright

A painting has a 3 dimensional texture to the paint, while a poster is inevitably flat. Different paint compositions will also reflect light differently, while a poster won't.

So, yeah, having the real painting has additional value.

I wouldn't pay much for a painting anyway. I have several paintings and posters up on the walls, and they're interesting for a time, and then I just don't see them anymore. They're just part of the wall.