HOWTO: Resize multiple files with ImageMagick tool ‘mogrify’

a) Pass all JPG-files in current directory (including subdirectories) to mogrify:

    find -name '*.jpg' -print0 | xargs -0 -r mogrify -resize 800x600

Options:

    -print0 -- used to process spaces in file names
    -r      -- suspends mogrify when there is nothing to do

b) Convert multiple PNG files into JPEG:

    mogrify -format jpg *.png

c) Resize to 50% percent of original:

    mogrify -resize 50% *.jpg

d) Resize to resolution YxZ only if image is greater than YxZ:

    mogrify -resize 2880x1800> *.jpg