This street art is painted by the very famous Italian graffiti artist Blu. It is said that the mural only took him 1 day to complete, but he was seen at the wall one day to inspect the wall, the next day to start painting and the third day to finish up. So the mural probably took him 2-3 days.
Notice that the chimney on top of the building is part of it as well as the end of the pencil.

It was painted as a part of the exhibition "Icons for Now".