Prawn

gistfile1.rb

    @pdf = Prawn::Document.new(:margin => 0, :skip_page_creation => true)
    images.each do |imagem|
      geo = Paperclip::Geometry.from_file(imagem)
      if geo.height >= geo.width
        size = [612, 792]
        @pdf.start_new_page(:page_size => "A4", :layout => :portrait)
       else
        size = [792, 612]
        @pdf.start_new_page(:page_size => "A4", :layout => :landscape)
      end
      @pdf.image imagem, :fit => size
    end
    
    render :text => @pdf.render, :content_type => "application/pdf; charset=ISO-8859-1"