(A picture of my cat teabagging my roommate's cat)
Instead of working, I decided to redo my Steam userpic to duplicate the style of the in-game NPC portraits in Left 4 Dead. You can also see it as my D-toid icon. Here's how I did it. I don't have numbers or anything, I just needed something to do to take my mind off work for a while, so I just twiddled the sliders until it looked right.
I took a side-lit portrait in my macbook's Photobooth and pulled it into Photoshop.
I cropped to a square image with similar proportions to the L4D portraits.
Then converted it to grayscale, then converted it back to RGB (so I could apply filters).
Adjusted brightness/contrast to wash it out a bit and then enhance the shadows.
I copied the original layer twice, for the filters.
Applied the Poster Edges filter to one layer to outline the shadows and contours.
Then applied the Watercolor filter to the other layer to flatten out the skin tones.
Adjusted the opacity of the filtered layers until it looked right.
Made a new layer to create the vignetting effect with a black feathered brush, sized to about 10% of the width of the image.
Applied the photo filter (Image -> Adjustments) to adjust the overall color to approximate the greenish-sepia tint to the original L4D portraits.
Finally, reduce the image size to about 120x120 (the actual portrait is about 80x80), and Steam/L4D will resize it once you set it as your Steam userpic.