Quickly create, edit, compose or convert images from the command line.
$ brew install imagemagick
convert image to width of 200, make it progresseive and reduce quality to 80%
$ convert -resize 200 -interlace Plane -quality 80
Run the same command above but for all images in a directory
$ for i in *.jpg; do convert -resize 200 -interlace Plane -quality 80 $i $i; done
Here is the site of all the commands: http://www.imagemagick.org/script/command-line-options.php