The following optimization is pretty useful to re-check and fix with a web analyzer (eg https://www.gtmetrix.com/).

If you need to serve scaled images or just convert them to any percentage or size, you can do the following.

• Install imagemagick:
  
  1	sudo apt-get install imagemagick

• Open a terminal and run this command in order to reduce the size 50%:
  
  1	convert -resize 50% source.png destination.jpg

  
  Also, you can specify the size explicitly:
  
  1	convert -resize 1024X768 source.png destination.jpg