ruby-thumbor

require 'ruby-thumbor'

image = Thumbor::Cascade.new('my-security-key', 'remote-image.com/path/to/image.jpg')
image.width(300).height(200).watermark_filter('http://remote-image.com/path/to/image.jpg', 30).generate

# url will contain something like:
# /2913921in321n3k2nj32hjhj3h22/remote-image.com/path/to/image.jpg

# Now you just need to concatenate this generated path, with your thumbor server url

require 'ruby-thumbor'

crypto = Thumbor::CryptoURL.new 'my-security-key'

url = crypto.generate(width: 200, height: 300, image: 'remote-image.com/path/to/image.jpg')

meta: bool # flag that indicates that thumbor should return only meta-data on the operations it would otherwise perform;

crop: [<int>, <int>, <int>, <int>] # Coordinates for manual cropping. The first item is the two arguments are the coordinates for the left, top point and the last two are the coordinates for the right, bottom point (thus forming the square to crop);

width: <int> # the width for the thumbnail;

height: <int> # the height for the thumbnail;

flip: <bool> # flag that indicates that thumbor should flip horizontally (on the vertical axis) the image;

flop: <bool> # flag that indicates that thumbor should flip vertically (on the horizontal axis) the image;

halign: :left, :center or :right # horizontal alignment that thumbor should use for cropping;

valign: :top, :middle or :bottom # horizontal alignment that thumbor should use for cropping;

smart: <bool> # flag that indicates that thumbor should use smart cropping;

filters: ['blur(20)', 'watermark(http://my.site.com/img.png,-10,-10,50)'] # array of filters and their arguments