rails helper for jQuery lazy load plugin * http://www.appelsiini.net/projects/lazyload

application_helper.rb

module ApplicationHelper
  def lazy_image_tag source, options = {}
    options['data-original'] = source
    if options[:class].blank?
      options[:class] = "lazy"
    else
      options[:class] = options[:class].to_s + " lazy"
    end
    image_tag 'image_grey.jpg', options
  end
end

• put jquery.lazyload.js to app/assets/javascript
• put 'image_grey.jpg' to app/assets/images
• $('img.lazy').lazyload()