Done entirely in Inkscape 0.40; my reference is a photo I took over the summer with ~TheLadyFox as my gracious model.
I originally started this simply as a morning warm-up exercise in a more typical "vector" style. Somewhere along the way my printmaking instincts kicked in and I nuked all the neat outlines, opting instead to build up the image with dark-on-light shapes as if it were a print. Pretty soon I realized I had something worth taking all the way to a finished piece.