to_xml.rb

def to_xml(options = {}, &block)
  thumbs = Proc.new do |opts|
    [:large, :thumb, :icon].each do |style|
      opts[:builder].tag!("thumbnail-#{style}", self.photo.url(style, false))
    end
  end
  default_options = {
    :procs => [thumbs],
    :except => [:photo_file_name, :photo_file_size, :photo_content_type, :photo_updated_at]
  }
  super(default_options.merge(options), &block)
end