Paperclip Post-Processing

  #Your resizing will warp (squash or stretch) images if they don't match
  # your dimensions.
  #To resize while maintaining aspect ratio, use "64x64>" - This will
  #result in either the width or the height = 64 and the other side will
  #be relatively smaller.
  #To resize with crop, use "64x64#" - This will result in both width and
  #height = 64 and the longer of the two will be cropped evenly on either
  #side.
  #You should usually use one of these unless you are very sure of the
  #aspect ratio of the images being uploaded.

  
  has_attached_file :photo,
                    :styles => { 
                          :original => "700x700#", 
                          :large => "433x433#",
                          :medium => "150x150#", 
                          :thumb => "68x68#" 
                    }
                      
  #...

  # Callback after styles processing (thumbnails). 
  # Use this to extract Exif metadata from the image
  def post_process_photo
    # only works with jpgs
    if photo.content_type == 'image/jpeg' || 'image/pjpeg'
      img_meta = EXIFR::JPEG.new(photo.queued_for_write[:original].path)
      return unless img_meta
      #logger.debug "Photo EXIF: #{img_meta.inspect}"
      self.camera_model = img_meta.model
      self.exposure_time = img_meta.exposure_time.to_s
      self.f_number = img_meta.f_number.to_s
      self.taken_at = img_meta.date_time
      # also have width and height. See http://exifr.rubyforge.org/api/index.html for details
    end
  end