Shell script to recursively optimize all image in the current directory. WARNING: THIS OVERWRITES YOUR ORIGINALS AND REMOVES METADATA!

optimizeimages.sh

#!/bin/sh
set -o errexit

PNGS=`find . -iname "*.png"`
JPGS=`find . -iname "*.jpg"`
TMP1="_TMP1.PNG"
TMP2="_TMP2.PNG"

echo "Optimizing PNG"
for PNG in ${PNGS}
do
	BEFORE=`stat -c %s ${PNG}`
	echo -n "	${PNG}: ${BEFORE} "
	cp ${PNG} ${TMP1}
	COLORS=`pngtopnm ${PNG} | ppmhist -noheader | wc -l`

	if [ "$COLORS" -lt 2 ]; then
		COLORS=2
	fi

	if [ "$COLORS" -lt 257 ]; then
		cat ${PNG} | pngquant ${COLORS} > ${TMP1}
	fi

	pngcrush -q -l 9 -brute -rem alla ${TMP1} ${TMP2}
	rm ${TMP1}
	optipng -quiet -o7 -out ${TMP1} ${TMP2}

	AFTER=`stat -c %s ${TMP1}`
	if [ "$AFTER" -lt "$BEFORE" ]; then
		mv ${TMP1} ${PNG}
		echo "--> ${AFTER}"
	else
		echo "(Already optimal)"
	fi

	rm -f ${TMP1} ${TMP2}
done

echo "Optimizing JPG"
for JPG in ${JPGS}
do
	BEFORE=`stat -c %s ${JPG}`
	echo -n "	${JPG}: ${BEFORE} "
	jpegtran -optimize -copy none ${JPG} > ${TMP1}
	AFTER=`stat -c %s ${TMP1}`

	if [ "$AFTER" -lt "$BEFORE" ]; then
		mv ${TMP1} ${JPG}
		echo "--> ${AFTER}"
	else
		echo "(Already optimal)"
	fi
	rm -f ${TMP1}
done

Just added jpeg optimization with jpetran, which is also lossless

Cheers, but pngquant had a bad affect on my alpha channel png files. They ended up looking terrible. pngquant is apparently lossy.

Please consider quoting every argument, especially with destructive commands like rm, so as to prevent space-in-file-name-related issues:

rm -f "$TMP1" "$TMP2"

Also, there are two mainstream extensions for JPEG files: jpg and jpeg.

I made an updated version of this with significant changes (including multi-threading) here:
https://github.com/mjc/optimizeimages.sh