When first I came across René Magritte’s famous painting, which says in French “This is not a pipe,” I was quite confused. Of course it is a pipe. Just look at the painting. I propose a simple test to check: put something in the pipe and smoke it. You can’t? Why not? If not a pipe, then what is it?
A meta-painting reminds the viewer that they are not looking at natural objects in the real world, they are looking at a painting. It’s astounding how readily we forget.