This is a pen and ink drawing (black rolling writer on BFK) made by CNC Machine. The pen paths followed the contours of the gray areas of the digital image used as a 'map'. The first contours drawn were those which were the darkest tones in the image. The pen more or less follows the outer contours, spiraling inward about 30 lines per inch. Then the contours of the two darkest tones toghther, then the three darkest tones, and so on until the contours of all non-white tones were drawn last.
Here's a detail of the cat's face:
The lines do an interesting job of approximating the gray-tones of the original image and leave those complex criss-crossed curvy contours on the paper which I think are very beautiful!
The drawing took about 8 hours to complete at about three inches per second -- over a mile of line on this 14 x 14 inch drawing!