def thumb
      @image = Tandem::Image.find_by_id(params[:id])
      @content = Tandem::Content::Image.new(image: @image)
      respond_to do |format|
        format.html { render layout: nil }# thumb.html.erb
      end
    end
def thumb
      @image = Tandem::Image.find_by_id(params[:id])
      @content = Tandem::Content::Image.new(image: @image)
      respond_to do |format|
        format.html { render layout: nil }# thumb.html.erb
      end
    end
GET /images/1/thumb
 GET /images/1/thumb.json
this method is deliberately forgiving to image id's that don't exist