Compress or Resize images in BASH

sudo apt-get install imagemagick

#!/bin/sh
 
if [ ! -d ./output ]; 
then
  mkdir output
fi
 
for item in *.jpeg;
do
  echo "Converting ${item%.jpeg}"
  convert ${item} -resize 1024 ${item%.jpeg}.png 5
done

see more options: https://www.imagemagick.org/script/convert.php