Trying to figure out polymorphic association with image to other items

app-controllers-images_controller.rb

  def new
    @image = Image.new
    respond_with @image
  end

app-models-image.rb

class Image < ActiveRecord::Base

  belongs_to :parent, :polymorphic => true

  has_attached_file :content,
                    :styles => {
                      :full => "800x800>",
                      :medium => "400x400>",
                      :list => "200x200>",
                      :thumb => "100x100#"
                    }
end

app-models-piece.rb

class Piece < ActiveRecord::Base

  belongs_to :project
  has_many   :images, :as => :parent

  validates_presence_of :name
end

app-views-images_form.html.erb

<%= form_for @image, :html => { :multipart => true } do |f| %>
<%= f.hidden_field :parent_id %>
<%= f.hidden_field :parent_type %>
<%= f.file_field :content %>
<%= f.submit %>
<% end %>

app-views-pieces-show.html.erb

<p class="button-right">
  <%= link_to "Edit Piece",
              edit_piece_path(@piece),
              :class => "button icon edit" %>
</p>

<p>
  <%= @piece.project.client.name %> &raquo;
  <%= @piece.project.name %> &raquo;
</p>

<h1><%= @piece.name %></h1>
<p><%= @piece.description %></p>

<% if @piece.images.empty? %>
  <p>
    This piece has no images in the system. Why don't you
    <%= link_to "add one?", new_client_project_piece_image_path(:piece_id => @piece.id, :project_id => @piece.project.id, :client_id => @piece.project.client.id) %>
  </p>
<% else %>
  <h2>Images in <%= @piece.name %></h2>
  <ul class="images">
    <%= render :partial => "images/image",
               :collection => @piece.images,
               :as => "image" %>
  </ul>
  <p>
    <%= link_to "Add another image", new_client_project_piece_image_path(:parent_id => @piece.id, :project_id => @piece.project.id, :client_id => @piece.project.client.id) %>
  </p>
<% end %>