The Times is reporting that one of Banksy‘s public art works, “Flower Girl,” which features the silhouette of a girl peering up at a security camera, is going to be auctioned soon by Julien’s Auctions in Beverly Hills, California. According to the Times, Banksy, a street artist from Britain, had stenciled the mural on a wall of a gas station in Los Angeles in 2008.
prior probability asks, doesn’t street art belong to the public, and if so, is this proposed auction legal?
Julien’s Auctions, via Associated Press
prior probability 
I guess the owner of the building owns the art done on their property. Street art would be on a public street or building and not a private building.
That is a good answer, but it is not the correct one. What if I own a canvas and some paint and brushes, and these supplies are then stolen by A, an artist who then uses them to create a valuable work of art. Yes, I still own the canvas and the paint, but A owns the rights to his artistic creation … the Napoleonic Code offers one solution to this problem (give the painting to the artist, but make him pay for my supplies) … What do you think of this solution?
I think this is a great solution Enrique. However there has to be a rule of property law that solves this question. I do agree with the Napoleonic Code.