ImageMagick

convert

http://www.imagemagick.org/script/convert.php

convert -density 200x200 -quality 60 -compress jpeg input.pdf output.pdf
convert -compress Zip -density 150x150 input.pdf output.pdf

convert image1.png image2.png image3.png -quality 100 -units PixelsPerInch -density 72x72 output.pdf

convert -geometry 350x300 *.jpg

resize800x600.sh

#!/bin/bash
for i in *.jpg;
do
j=${i//\.jpg/};
convert -size 800x600 $i ${j}_800x600.jpg;
done

resize350x300.sh

#!/bin/bash
cd /var/www/ebay
for i in *.jpg;
do
j=${i//\.jpg/};
convert -geometry 350x300 $i ${j}_350x300.jpg;
mv *350x300.jpg 350x300/
done