{% load thumbnail %}
{% thumbnail content.forced_picture.image "500x333" as preview %}
  <a title="{{content.title}}"
     href="{{ content.file.get_absolute_url }}"
     class="image-block image-block-preview image-block-content">
    <img title="{{content.title}}"
         alt="{{content.title}}"
         src="{{ preview.url }}" />  
  </a>
{% endthumbnail %}
