As I said, I should be allowed to do this.  I see "impersonations" of famous works, mockeries, parody, where you can easily tell which famous work is the subject matter; I don't think artists need permission to do this.

Really, if I sell that drawing of mine where I "emulated" Giorgio de Chirico's painting, I'm going to have someone from his estate threatening legal action?

And photographs on the internet--how would anyone be able to tell which photograph, specifically, I took from?  What would a collage artist do?