(Image via alexandreorion.com/ossario)
Reverse Graffiti is the art of scraping, scrubbing, and pressure-hosing away dirt to create art.
Alexandre Orion of São Paulo, Brazil, scraped the skulls above in a traffic tunnel as a commentary upon the pollution humans were creating. Of course, the city tried to clean away his artwork, but in trying to do so, they found the only solution was to clean the entire tunnel!