Funny but difficult quizz.
Even the middle image is hard to tell. Possibly edge detection filter (Canny) followed by thresholding (without non-maxima suppression).
The right one is really unexpected. Looks like anisotropic smoothing (edge flow) followed by edge detection followed by vectorization (looks like short line segments rather than free contours).
Anyway, the structures on the right image bear little resemblance with the original content and introduce many artifacts, as an overlay shows.
http://xmages.net/i/3255881[
^]
Other hypotheses:
- isophotes on the smoothed image, because the curves are bundled, followed by some postprocessing, because large portions are missing;
- postprocessing could be polylines fitted to isophotes in a snake-like fashion.