RandomImage

$ rails generate random_image:install

/config/initializers/random_image.rb

config.register_catalog do |catalog|
  catalog.path = "#{Rails.root}/catalog_name"
  catalog.name = :catalog_sym
end

/config/routes.rb

random_image_for :catalog_sym, 'random_image'

random_image_catalog_sym_path

.random-image {
  background-image: random_image_catalog_sym();
}