Batch scale images to a particular size

First install imagemagick:

sudo apt-get install imagemagick

Then CD into the directory containing the images and make a new directory that will hold all the re-sized images. In this case I called it resized:

mkdir resized

Then run the command (from the directory holding the original images):

find . -iname \*.jpg -exec convert -verbose -quality 80 -resize 1600x1200 "{}" "resized/{}" \;

The above command will find (recursively) all the jpg files in the current directory and all directories in it, then it will execute the covert command on each image and finally store the scaled image in the resized directory. You can adjust the size parameters, file extensions and target directory as you desire.