Run all images in wp-content/uploads through lossless compression.

compress-images-in-wp-uploads.bash

# PNG files: optipng
find wp-content/uploads -name '*.png' -exec optipng {} +

# JPG files: jpegtran
find wp-content/uploads -name '*.jpg' -o -name '*.jpeg' | xargs -I{} jpegtran -copy none -optimize -outfile {} {}

# Webp: cwebp
find wp-content/uploads -name '*.webp' -exec cwebp -lossless {} -o {} \;

# GIF: gifiscle
find wp-content/uploads -name '*.gif' -exec gifsicle -O3 -b {} \;