Doesn't really seem like graffiti when people are actually cleaning up the walls rather than painting on them, but there it is - reverse graffiti in South Africa. Inspired by the works of Paul Curtis (a reverse graffiti pioneer), a group of students in South Africa led by Martin Pace decided to clean up their town and scrub pictures into dirty walls. They've done a number of projects now, and really, the effect is quite beautiful.
Pace's first scrubbed wall was a dirty highway wall, where he used a metal brush to scrub a pictorial timeline of his town's architecture. Then he enlisted a few friends to help - Stathi Kongianos, JP Jordaan and Nick Ferreira, and they went to town on a number of other walls in the area. Among their accomplishments is a beautiful mural of trees and a giant “Sardine Run” (featuring a school of stencilled fish) swimming across a city bridge.
Since reverse graffiti isn't adding any new paint, it's not really illegal, especially since they're cleaning up the city's surfaces and not making them dirty. Of this fact, Pace said, “That’s the beauty of the whole project. We have had council guys in police cars stop us in the middle of the day while we are working and asking us if we have been commissioned to do this and when we answered no, they gave us thumbs up and said keep doing what you are doing.”