I had a spare sheet of corrugated cardboard left over from my sketchbook instructable
and I had an assignment where we had to make a self portrait in art class. So, I saw on the internet
where someone had cut away the top layer of paper which allowed the corrugations underneath to show. I thought that it would be cool if I made a self portrait by using that method, so I took an image of my face, edited it so that it was only black and white (no gray), printed it, and removed the black parts with an x-acto knife. I was lucky that my stencil image didn't have any islands I had to remove. Once I finished the stencil, I simply transferred it onto the scrap of cardboard, cut along the lines with the x-acto, and peel off the top layer of paper. Finally, I painted the corrugations black to make the portrait easier to distinguish.
This basically takes advantage of negative space filling in the rest of the portrait. The negative space fools the brain into figuring where lines begin and end and helps give a sense of depth to the image.
As a positive benefit of doing this, you get a pretty awesome stencil of yourself (or whatever you want) that you can personalize anything you want with.