An interesting variant of the line-halftoning idea is to constrain the ways in which the lines can move. In the above image, a set of vertical parallel lines are allowed to squiggle sideways so that
together they approximate the local grayscale of the image. You might have to blur your eyes a bit and step back from the monitor to get the effect.
This approach is a bit dicey, since the average grayscale of any given line is constant, so it tends to wash out the image. And it fails (though sometimes in visually interesting ways) on high contrast images.
Nuther one here.
I'm planning to use the lines as base geometry for more fanciful Renderman-based images -- one thought I had was to mimic wood grain, so it would look like the image of Lena was revealed in a sawn log. Hm. Maybe a picture of the Virgin Mary would be more thematically appropriate....