Cloudinary + Carrierwave + Heroku + Railsでの画像を手軽に利用する方法 ref: http://qiita.com/GenTamura84/items/38cf899827bba050a21c

_form.html.erb

<%= form_for(@user) do |f| %>
  <% if @user.errors.any? %>
    <div id="error_explanation">
      <h2><%= pluralize(@user.errors.count, "error") %> prohibited this user from being saved:</h2>

      <ul>
      <% @user.errors.full_messages.each do |msg| %>
        <li><%= msg %></li>
      <% end %>
      </ul>
    </div>
  <% end %>

  <div class="field">
    <%= f.label :name %><br />
    <%= f.text_field :name %>
  </div>
  <div class="field">
        <%= image_tag(@user.avatar_url(:thumbnail), :width => 80, :height => 80) %>
        <%= f.file_field :avatar %>
        <%= f.check_box :remove_avatar %> 画像を削除する
        <%= f.hidden_field :avatar_cache %>
  </div>
  <div class="actions">
    <%= f.submit %>
  </div>
<% end %>

avatar_uploader.rb

# encoding: utf-8
class AvatarUploader < CarrierWave::Uploader::Base

  include Cloudinary::CarrierWave

  process :convert => 'png'
  process :tags => ['avatar']

  version :standard do
    process :resize_to_fill => [100, 150, :north]
  end

  version :thumbnail do
    process :resize_to_fit => [50, 50]
  end

  def public_id
    return model.id ・・・※1
  end

end

console

$heroku open

gemfile

source 'https://rubygems.org'

gem 'rails', '3.2.8'

gem 'carrierwave'
gem 'cloudinary'

gem 'heroku'

group :test, :development do
    gem 'sqlite3'
end

group :production do
    gem 'pg'
    gem 'thin'
end

group :assets do
  gem 'sass-rails',   '~> 3.2.3'
  gem 'coffee-rails', '~> 3.2.1'
  gem 'uglifier', '>= 1.0.3'
end

gem 'jquery-rails'

index.html.erb

<h1>Listing users</h1>

<table>
  <tr>
    <th>Name</th>
    <th></th>
    <th></th>
    <th></th>
  </tr>

<% @users.each do |user| %>
  <tr>
    <td><%= user.name %></td>
    <td><%= link_to 'Show', user %></td>
    <td><%= link_to 'Edit', edit_user_path(user) %></td>
    <td><%= link_to 'Destroy', user, method: :delete, data: { confirm: 'Are you sure?' } %></td>
  </tr>
<% end %>
</table>

<br />

<%= link_to 'New User', new_user_path %>

routes.rb

CloudinaryDemo::Application.routes.draw do
  resources :users

  root :to => 'users#index'  
end

show.html.erb

<p id="notice"><%= notice %></p>

<p>
  <b>Name:</b>
  <%= @user.name %>
</p>

<p>
  <b>Avatar:</b>
  <%= image_tag(@user.avatar_url) %>
</p>


<%= link_to 'Edit', edit_user_path(@user) %> |
<%= link_to 'Back', users_path %>

user.rb

class User < ActiveRecord::Base
  attr_accessible :avatar, :avatar_cache, :name, :remove_avatar

  mount_uploader :avatar, AvatarUploader

end