#Installation
brew install imagemagick
brew install ghostscript
brew install ufraw
netpbm dcraw
#Convert all .NET image extensions to .JPG
for img in *.NEF; do convert "$img" "$img.jpg"; done
source: http://superuser.com/a/577661
#Batch resize of images in a folder cd to the directory where your images are located (temp) after creating a new directory to hold the changed files (say, temp2)
mogrify -path ./temp2/ -resize 40x40% -quality 60 -format jpg *.jpg
this will take all png files in your current directory (temp), resize to 60% (of largest dimension and keep aspect ratio), set jpg quality to 60 and convert to jpg.
source: http://www.imagemagick.org/discourse-server/viewtopic.php?t=14587