I've figured out some of what I want to do here, so I can be more
This create action adds each uploaded Image, then creates a thumnail of
each and stores it in the @temp_thumb_data array.
@artwork = @current_user.artworks.new params[:artwork]
params[:image_data].each do |file|
@artwork.images << Image.new( :uploaded_data => file ) if file.size
end unless not params[:image_data]
@temp_thumb_data = 
@artwork.images.each do |image|
image.with_image do |img|
@temp_thumb_data << img.thumbnail(100, 100).to_blob
However it is stored as an encoded string and can thus not simply be
displayed. The normal method would be to use send_data in another
action, but I can't do that here because the uploaded file is not being
persisted and would not be available to the other action.