new_contents: from django import template
  from django_images.settings import IMAGE_SIZES
  from django_images.templatetags import images
  
  register = template.Library()
  
  
  @register.filter
  def at_size_with_fallback(image, size):
      if not image:
          if not size in IMAGE_SIZES:
              raise ValueError("Received unknown size: %s" % size)
          w, h = IMAGE_SIZES[size]['size']
          return 'http://placekitten.com/%d/%d/' % (w, h)
      return images.at_size(image, size)
  
subject: Add missing template tags