Here is an excellent use of a wall, an air vent, and paint to drive home a point.

Friends of the Earth Korea sponsored a provocative mural of “Dark Smoke”. It’s an ominous work of public art that’s message clearly emerges through the billowing smoke: “You’re gonna reap what you sow.”

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The caption reads:

In order to communicate the message that the polluted air by human finally returns to human, we did a wall painting on the outside of a building with 3.8 x 2.5m by using water paints.

via Ads of the World