# File lib/FileCache.rb, line 94
  def random_file_system_image(collection_type=nil)
    all_image_urls=file_system_image_urls_in_cache    
    all_image_urls.length.times do
      begin
        index=rand(all_image_urls.length)
        image=get_file_system_image(all_image_urls[index%all_image_urls.length])
        return image if ((collection_type==nil) || (image.send(collection_type).length>0))
      rescue #silently swallow any exception
      end    
    end
    raise 'no suitable image found in cache'
  end