## photo_meta.rb

module PhotoMeta
  def self.new(data)
    return YAML.load(data)
  end
end

## photo.rb

class Photo < ActiveRecord::Base
  has_attachment :storage => :file_system

  composed_of :meta, :class_name => 'PhotoMeta', :mapping => [%w(meta_data to_yaml)]

  after_resize do |record,img|
    if record.meta_data.blank?
      record.meta = MiniExiftool.new(record.temp_path, :composite => true)
      record.caption = record.meta.headline
      record.description = record.meta.description
      record.tag_list = record.meta.keywords
    end
  end
end