TemplateSyntaxError Invalid filter: 'thumbnail_url'

Environment:

Request Method: GET
Request URL: http://localhost:8000/318-accesorios-para-autos/2-bateria-tipo-65ah-herbo

Django Version: 1.9.9
Python Version: 2.7.12
Installed Applications:
['django.contrib.admin',
 'django.contrib.auth',
 'django.contrib.contenttypes',
 'django.contrib.gis',
 'django.contrib.messages',
 'django.contrib.sessions',
 'django.contrib.sites',
 'django.contrib.staticfiles',
 'django.contrib.humanize',
 'django.contrib.flatpages',
 'bootstrapform',
 'pinax_theme_bootstrap',
 'pinax_theme_bootstrap_account',
 'annoying',
 'account',
 'metron',
 'eventlog',
 'treebeard',
 'django_extensions',
 'cities_light',
 'dal',
 'dal_select2',
 'easy_thumbnails',
 'image_cropping',
 'floppyforms',
 'feedback',
 'analytical',
 'dbbackup',
 'django_nose',
 'rest_framework',
 'rest_framework.authtoken',
 'corsheaders',
 'radpress',
 'newsletter',
 'django_summernote',
 'sorl.thumbnail',
 'preciosa',
 'preciosa.precios',
 'preciosa.voluntarios',
 'preciosa.datos',
 'preciosa.acuerdos',
 'preciosa.api',
 'preciosa.flatpagex']
Installed Middleware:
['django.middleware.common.CommonMiddleware',
 'django.contrib.sessions.middleware.SessionMiddleware',
 'django.middleware.csrf.CsrfViewMiddleware',
 'django.contrib.auth.middleware.AuthenticationMiddleware',
 'django.contrib.messages.middleware.MessageMiddleware',
 'django.contrib.flatpages.middleware.FlatpageFallbackMiddleware',
 'corsheaders.middleware.CorsMiddleware']

Template error:
In template /code/preciosa/templates/precios/detalle_producto.html, error at line 60
   Invalid filter: 'thumbnail_url'   50 :                                 </tr>
   51 :                                 {% endfor %}
   52 :                             </table>
   53 : 
   54 :                             {% if prods_similares %}
   55 :                             <br />
   56 :                             <h4>Productos similares</h4>
   57 :                             <ul class="list-group">
   58 :                             {% for prod in prods_similares %}
   59 :                             <li class="list-group-item">
   60 :                                 <img alt="" src=" {{ prod.foto|thumbnail_url:'small' }} ">
   61 :                                 <a href="{{ prod.get_absolute_url }}">{{ prod.descripcion }}</a>
   62 :                             </li>
   63 :                             {% endfor %}
   64 :                             </ul>
   65 : 
   66 :                             {% endif %}
   67 :                         </div>
   68 :                         {% comment %}
   69 :                         <div class="comment-text">
   70 :                             Awesome design

Traceback:

File "/usr/local/lib/python2.7/dist-packages/django/core/handlers/base.py" in get_response
  174.                     response = self.process_exception_by_middleware(e, request)

File "/usr/local/lib/python2.7/dist-packages/django/core/handlers/base.py" in get_response
  172.                     response = response.render()

File "/usr/local/lib/python2.7/dist-packages/django/template/response.py" in render
  160.             self.content = self.rendered_content

File "/usr/local/lib/python2.7/dist-packages/django/template/response.py" in rendered_content
  135.         template = self._resolve_template(self.template_name)

File "/usr/local/lib/python2.7/dist-packages/django/template/response.py" in _resolve_template
  90.         new_template = self.resolve_template(template)

File "/usr/local/lib/python2.7/dist-packages/django/template/response.py" in resolve_template
  80.             return select_template(template, using=self.using)

File "/usr/local/lib/python2.7/dist-packages/django/template/loader.py" in select_template
  62.                     return engine.get_template(template_name, dirs)

File "/usr/local/lib/python2.7/dist-packages/django/template/backends/django.py" in get_template
  40.             return Template(self.engine.get_template(template_name, dirs), self)

File "/usr/local/lib/python2.7/dist-packages/django/template/engine.py" in get_template
  190.         template, origin = self.find_template(template_name, dirs)

File "/usr/local/lib/python2.7/dist-packages/django/template/engine.py" in find_template
  157.                         name, template_dirs=dirs, skip=skip,

File "/usr/local/lib/python2.7/dist-packages/django/template/loaders/base.py" in get_template
  46.                     contents, origin, origin.template_name, self.engine,

File "/usr/local/lib/python2.7/dist-packages/django/template/base.py" in __init__
  189.         self.nodelist = self.compile_nodelist()

File "/usr/local/lib/python2.7/dist-packages/django/template/base.py" in compile_nodelist
  231.             return parser.parse()

File "/usr/local/lib/python2.7/dist-packages/django/template/base.py" in parse
  516.                     raise self.error(token, e)

Exception Type: TemplateSyntaxError at /318-accesorios-para-autos/2-bateria-tipo-65ah-herbo
Exception Value: Invalid filter: 'thumbnail_url'
mgaitan / preciosa

TemplateSyntaxError Invalid filter: 'thumbnail_url' #257
