ppmspread - displace a PPM image's pixels by a random amount
ppmspread amount [ppmfile]
This program is part of Netpbm(1).
ppmspread reads a PPM image as input and moves every pixel around a random bit relative to its original position. amount determines by how many pixels a pixel is to be moved around at most.
Pictures processed with this filter will seem to be somewhat dissolved or unfocussed (although they appear more coarse than images processed by something like pnmconvol).
The randomness in the image is limited before Netpbm 10.37 (December 2006) -- if you run the program twice in the same second, you may get identical output.