Sometimes you only want the original images and not the generated sizes <name-of-image>-150x150.png. This command deletes all the files with a certain pattern in the file name. See https://silvanhagen.com/wordpress-delete-generated-images/ for more details.

delete-generated-wp-images.sh

# List the files
find -E . -type f -regex ".*-[[:digit:]]{2,4}x[[:digit:]]{2,4}(@2x)?.(jpg|jpeg|png|eps|gif)"

# DANGER! Delete the files 
find -E . -type f -regex ".*-[[:digit:]]{2,4}x[[:digit:]]{2,4}(@2x)?.(jpg|jpeg|png|eps|gif)" -delete

# If your OS doesn't support -E (tip from https://github.com/quasel)
find . -type f -regextype posix-extended -regex ".*-[[:digit:]]{2,4}x[[:digit:]]{2,4}(@2x)?.(jpg|jpeg|png|eps|gif)"

# Improved with the help of https://github.com/markhowellsmead

wp-cli-regenerate-media.sh

# Regenerate all media files and sizes
wp media regenerate --yes

# empty space for copying