Use ImageMagick to compress JPEG, resizing longest side to 2000 pixels (maintains aspect ratio):
convert Shrouded.jpg -sampling-factor 4:2:0 -strip -quality 85 -interlace JPEG -resize '2000x2000' image_converted.jpg
Or do the same thing but modify files in place:
cd images/to/convert
mogrify -sampling-factor 4:2:0 -strip -quality 85 -interlace JPEG -resize '2000x2000' *.jpg
This does a decent job of compressing PNGs (only tested on a stylized graphic):
pngquant -o out.png teton_splash_resized.png --force --quality=0-20
Basically, max-height as a percentage is a percentage of the parent's actual height (not max-height).
If the parent has set only max-height and not height, max-height of the child becomes none,
which allows it to be as tall as possible.