You can persecute graffiti painters - "Please, Mr. Officer, it is art" usually doesn't count as much of an argument - but what do you do with Reverse Graffiti?
The painter in the picture - Brazilian Alexandre Orion - creates his art by cleaning walls. His haunting designs are - literally - painted in the dirt.
His technique created quite a lot of confusion amongst the authorities of Sao Paulo. While it would have been possible to persecute him and/or prohibit him from painting had he been doing traditional graffiti, there was no legal possibility to stop him from partially cleaning particularly dirty walls. What they finally did was scrub the walls of the tunnel where Alexandre had been painting completely blank - and, subsequently, scrub the walls of ALL tunnels in Sao Paulo.