Perform operations on multiple images, such as resizing, cropping, flipping, and adding effects. Changes are applied directly to the original file. Part of ImageMagick. More information: https://imagemagick.org/script/mogrify.php.
mogrify -resize 50% *.jpg
DSC
to 800x600:mogrify -resize 800x600 DSC*
mogrify -format jpg *.png
mogrify -modulate 100,50 *
mogrify -modulate 200 *