Highest minification with pngcrush

pngcrush.sh

# single image
pngcrush -rem alla -brute -reduce src.png dest.png

# directory of images
pngcrush -rem alla -brute -reduce -d outputdir ./*.png

pngrush-directory.sh

# adapted from http://davidwalsh.name/pngcrush-directory

#!/bin/sh
for png in `find $1 -name "*.png"`; do;  pngcrush -rem alla -brute -reduce "$png" temp.png; mv -f temp.png $png; done