sudo apt-get install imagemagick

convert  -resize 50% source.png dest.jpg

convert  -resize 1024X768  source.png dest.jpg

sudo apt-get install imagemagick

mogrify -resize 50% *.png      # keep image aspect ratio
mogrify -resize 320x240 *.png  # keep image aspect ratio
mogrify -resize 320x240! *.png # don't keep image aspect ratio
mogrify -resize x240 *.png     # don't keep image aspect ratio
mogrify -resize 320x *.png     # don't keep image aspect ratio

mogrify -resize 320x240 *.jpg

mogrify -resize 320x240! *.jpg

sudo apt-get install imagemagick

mogrify -verbose -resize '40%' *.JPG

convert -resize 50% myfigure.png myfigure.jpg

convert myfigure.png -resize 200x100 myfigure.jpg

sudo apt-get install phatch

sudo add-apt-repository ppa:vfrico/stable
sudo apt-get update
sudo apt-get install pimagizer