I've been using this great imagemagick script for optimizing images the past few years. Works like a charm. Any images that are going to be served from my websites first get optimized via the script.

  smartresize() {
      mogrify -path $3 -filter Triangle -define filter:support=2 -thumbnail $2 -unsharp 0.25x0.08+8.3+0.045 -dither None -posterize 136 -quality 82 -define jpeg:fancy-upsampling=off -define png:compression-filter=5 -define png:compression-level=9 -define png:compression-strategy=1 -define png:exclude-chunk=all -interlace none -colorspace sRGB $1
  }

Usage:

  smartresize image.png 300 outdir/
  

Looks like I must have found it here https://www.smashingmagazine.com/2015/06/efficient-image-res...