This program is part of Netpbm.
ppmshift reads a PPM image as input. Shifts every row of image data to the left or right by a random amount, within a range of shift pixels. The random distribution is uniform, centered at zero movement.
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.
This is another one of those effects I intended to use for MPEG tests. Unfortunately, this program will not help me here - it creates too random patterns to be used for animations. Still, it might give interesting results on still images.
Check this out: Save your favourite model's picture from something like alt.binaries.pictures.supermodels (ok, or from any other picture source), convert it to ppm, and process it e.g. like this, assuming the picture is 800x600 pixels:
#take the upper half, and leave it like it is
pamcut -top=0 -width=800 -height=300 cs.ppm >upper.ppm
#take the lower half, flip it upside down, dim it and distort it a little
pamcut -top=300 -width=800 -height=300 cs.ppm | \
pamflip -topbottom | \
ppmdim 0.7 | \
ppmshift 10 >lower.ppm
#and concatenate the two pieces
pnmcat -topbottom upper.ppm lower.ppm >newpic.ppm
The resulting picture looks like the image being reflected on a water surface with slight ripples.