How did Andy Warhol deal with such things, I wonder. Did he obtain rights?
Warhol was sued over the flowers picture he stole from a science textbook.
The difference between what Zimmerman did and that of Fairey and Warhol is that Zimmerman painted his interpretation of the image. The others manipulated copies of the photos they used (scanned a picture and printed it with factory reproduction techniques).
There are lawsuits when “sports painters” do this but they are making several copies of the same thing. If you are “one and done” there is generally more tolerance in the courts for your actions.