Perhaps you don't recognize it by its name, but certainly you've seen some work made with the 'Stop-motion' technique. This techique is an extremelly laborious type of animation, where objects are photographed, frame by frame. Between each frame, the object's position is moved slightly, so when the film is shot you get the feeling the objects are actually in motion. Although it seems rather archaic, thousands of comercials and movies are produced using this method, most notably the animation picture Chicken Run (2000).
Now try to imagine using this techique using graphite, paint and a city's walls. Apart from being a totally insane amount of work, the results are simply ingenious and inspired! This is exactly what Blu did in the movie Muto. Blu paints, photographs, paints over, photographs again, and so on. And on! Filmed in the streets, or, actually, walls of Buenos Aires and its outskirts, the artist had a monstrous amout of work. Although with some assistance, many were the hours needed to reach the desired product and effect. Furthermore, Blu also does drawings, illustrations, murals, always filled with criticism and inspired by urban life.
If you have the time, don't forget to watch this video. Muto runs for little more than seven minutes, but captures your attention and amazes you for the amount of work it comprises.