The look of a document put through a photocopier a few too many times: harsh black lines, blown-out whites, and no midtones at all.
Two things are combined. A difference-of-blurs finds the edges, which becomes the ink outline. Separately, anything below a brightness threshold is filled in solid, which is what a photocopier does to shadows. The two are combined by taking whichever is stronger.
The final step is what makes it convincing: the result is mapped onto exactly two colours, inkColor and paperColor. No pixel in the output is a shade of the original picture. Everything is ink, paper, or a blend of the two.
detail sets the size of the blur and so how coarse the edges it catches are. darkness pushes both the line weight and how much of the shadow fills in.