gistfile1.rb

require 'rubygems'
require 'open-uri'
require 'hpricot'

def find_biggest_image_url(url)
  page = Hpricot(open(url))
  
  biggest_image_url = nil;
  biggest_image_area = 0;
  
  page.search('img') do |img|
    width = img.attributes['width'].to_i
    height = img.attributes['height'].to_i
    area = width * height
    
    if area > biggest_image_area
      biggest_image_area = area
      biggest_image_url = URI.parse(url).merge(img.attributes['src'])
    end
  end
  
  biggest_image_url
end

puts find_biggest_image_url('http://www.touchmyapps.com/2009/04/03/the-void-in-review-the-space-between/')
puts find_biggest_image_url('http://en.wikipedia.org/wiki/U2')