He is removing the white line. The world turns darker as the cop paints more, as after removing all other colors from the world, the cop will finally go after white, and there will be only darkness.

(this is why you pay artists to make art for you, and not just ask a computer system to generate something, artists understand what you are trying to say. (for me the image also seemed to imply the cop was moving from left to right) The selection of the image also torpedoes his whole 'I love punk rock' thing, it is a failure on so many levels you could write an entire essay on it, esp if you include the fact that nobody on LW seems to have noticed or cared enough to say something about it.).