Simulate old bw photo printing effect

[Ofnuts]

Several ways to do that:

1. The Engrave filter
   
2. My old luminosity-tiler script: you replace the image by tiles that have the same equivalent luminosity, if tiles are 1px wide and contain a widening group of black pixels, the result is lines of varying width.
   
3. My more recent ofn-engraving script.