mix handlebars with erb

Question

In Rails 3.2 I was able to rename a extension to .handlebars.erb in order to be able to use erb tags (mainly <%= image_tag 'image.jpg' %>) in my handlebars templates.

I'm unable to get this going in Rails 4. Im using

gem 'ember-rails'
gem 'handlebars-source'

The error I'm getting:

undefined method `image_tag'

The view in question is the one below, same for any other view:

<div class="row-fluid">
  <div class="span12">
    <div class="row-fluid distance_0">
      <div class="row-fluid divider slide_divider base_color_background">
        <div class="container">
          <span class="bottom_arrow"></span>
        </div>
      </div>

      <!-- Title and Description -->
      <div class="row-fluid slide_content fullwidth">
        <div class="container">
          <div class="row-fluid text_bar_pattern themeple_sc">
            <div class="content_bar">
              <h3>
              </h3>
              <p>
              </p>
            </div>
            {{#linkTo "user.new" class="button_bar"}}{{/linkTo}}
          </div>
        </div>
      </div>
      <div class="row-fluid">
        <div class="container">
          <div class="bottom_shadow_full"></div>
        </div>
      </div>

      <div class="row-fluid distance_2"></div>
      <div class="row-fluid distance_2"></div>
      <div class="row-fluid">
        <div class="container">
          <img src="images/old_letters_blur.jpg" alt="">
        </div>
      </div>

      <%= image_tag 'old_letters_blur.jog' %>

      <!-- TextBar -->
      <!-- TextBar End -->

    </div>
  </div>
</div>

Any suggestions?