MacLife has an article on the scriptable images processing systems, or sips. sips is very powerful, but it also has a really simple syntax. To duplicate my one-liner for imageworsener, all you would need is: sips –resampleHeight 33 *.png
I used to use imagemagick for resizing in the command line, but imageworsener has a much cleaner syntax. Use this to resize the height all pngs to 33 pixels: for i in $( ls *.png); do imagew -height 33 $i re_$i; done If you’re on Mac OS X, you can install imageworsener through Homebrew.