class Image < ActiveRecord::Base
  belongs_to :gallery

...

def file=(incoming_file)
  @temp_file = incoming_file
  @filename = incoming_file.original_filename
  if !incoming_file.original_filename.blank?
     # Make sure the directory exists for us to save into
     FileUtils.mkdir_p(File.expand_path("public/images", RAILS_ROOT))

     # Set file to unique timestamp plus original extension
     self.path = "/images/#{@gallery}." + incoming_file.original_filename.gsub(/.*\./, '')
     File.open(self.absolute_path(:original), File::CREAT|File::WRONLY) { |f| f.write(incoming_file.read) }
  end
end

...
end