# Gemfile
    gem "refile", require: "refile/rails"
    gem "refile-mini_magick"

# bash
    brew install imagemagick # OS X
    sudo apt-get install imagemagick # Ubuntu

    rails generate migration add_profile_image_to_users profile_image_id:string
    rake db:migrate

# app/models/user.rb
    class User < ActiveRecord::Base
      attachment :profile_image, type: :image
      attachment :resume, extension: ["pdf", "doc"]
    end

# app/views/users/_form.html.erb
    <%= form_for @user do |f| %>
      <%= f.attachment_field :profile_image %>
    <% end %>

# app/controllers/users_controller.rb
    def user_params
      params.require(:user).permit(:profile_image)
    end

# app/views/users/show.html.erb
    <%= image_tag attachment_url(@user, :profile_image, :fill, 300, 300, format: "jpg") %>