I want to implement lightbox2 => http://lokeshdhakar.com/projects/lightbox2/ I have downloaded the files and add it to vendor/assets/javascript vendor/assets/stylesheets and vendor/assets/img ==> (that's a folder that comes with lightbox)

_gallery.hml.erb

<div class="image-row">
   <div class="image-set">
     <% Image.all.each do |i| %>
     	<a class="without-caption image-link" data-lightbox="image-1" rel="shadowbox" href="<%=i.image.to_s %>" title="<%= i.caption %>">
        <%= image_tag i.image.url(:thumb) %>
        </a>
     <% end %>  
   </div>
</div>

application.css

/*
 * This is a manifest file that'll be compiled into application.css, which will include all the files
 * listed below.
 *
 * Any CSS and SCSS file within this directory, lib/assets/stylesheets, vendor/assets/stylesheets,
 * or vendor/assets/stylesheets of plugins, if any, can be referenced here using a relative path.
 *
 * You're free to add application-wide styles to this file and they'll appear at the top of the
 * compiled file, but it's generally better to create a new file per style scope.
 *
 *= require_self
 *= require_tree .
 *= require lightbox
 */

application.html.erb

  <title>Project</title>
   <%= stylesheet_link_tag "styles", "lightbox", media: "all", "data-turbolinks-track" => true %>
   <%= javascript_include_tag "application", "data-turbolinks-track" => true %>
   <%= csrf_meta_tags %>
</head>

application.js

//= require jquery
//= require lightbox-2.6.min
//= require jquery_ujs
//= require turbolinks
//= require_tree .