download all images from a web page via img src using nokogiri and mechanize

downloader.rb

require 'rubygems'
require 'nokogiri'
require 'open-uri'
require 'uri'
require 'mechanize'
require 'pathname'

# inspired by: http://stackoverflow.com/a/7933585/281699
class Downloader
  def make_absolute href, root
    URI.parse(root).merge(URI.parse(href)).to_s
  end

  def get_images_from_url url, destination='~/Desktop/nest'
    begin
      webpage = Nokogiri::HTML(open(url))
    rescue OpenURI::HTTPError => e
      if e.message == '404 Not Found'
        puts "Not Found"
        return
      else
        raise e, "#{e.message}"
      end
    rescue => e
      raise e, "#{e.message}"
    end

    webpage.xpath("//img/@src").each do |src|
      uri = make_absolute(src,url)
      final_destination = File.join(File.expand_path(destination), File.basename(uri))
      begin
        next if File.exists? final_destination
        puts "Getting: #{uri}"
        agent = Mechanize.new
        agent.get(uri).save final_destination
      rescue => e
        puts "The request for a page at #{uri} returned an error. #{e.message}"
        next
      end
    end
  end
end

URLs = [
      'http://example.com'
    ]

URLs.each do |url|
  Downloader.new.get_images_from_url url
end