Ruby sips
sips is an extremely fast image processing utility that ships with OS X. It is not nearly as robust as, say, ImageMagick, but therein lies its beauty.
rsips seeks to expand on sips (but not too much) and might prove to be helpful in your everyday scripting, Rakefiles, static compilers, etc.
Install
gem install rsips
Basic Usage
require 'rsips'
image = Rsips::Image.new("photo.jpg")
# => @width = "580", @height = "870"
image.vertical? # => true
Long edge resizing
image.resize 300
# => @width = "200", @height => "300"