I love this picture from Alec Soth's new series for the Times, umpteen portraits of workers in Rockford, Illinois.
As the camera recorded the portrait, the snow recorded the process of the portrait.
The tracks tell the story: Bloomingdale stepping lightly, perhaps tentatively, into the frame from the lower right corner, turning and facing the camera. Soth — or his assistant — more comfortably tromping from camera to subject, likely more than once, loop-de-looping to Bloomingdale and back to meter him or hand him a color-checker chart to hold for a frame or brush lint off his jacket or help him with his stance.
All the usual business of making a portrait, rarely seen in the final image, but here made visible for us by the snow.
Story: http://www.nytimes.com/interactive/2011/01/23/magazine/rockford.html
Backstory: http://lens.blogs.nytimes.com/2011/01/19/rockfords-group-portrait-in-five-days/