> In this sense what Warhol has done is transformative.

Where is the line between blatant copying and transformation? If I take some photograph and just change colors can I claim I changed the photo's perception and thus sent a unique message? Maybe, but it's all about ideas in my head, not the changed photo itself. Same goes about many Warhol's works. They are just slightly changed copies of someone else copyrighted works and must be accompanied by art critiques explanations to be appreciated in full.