old_contents: # Based on http://djangosnippets.org/snippets/1580/
  from django import forms
  
  
  class ImageWidget(forms.FileInput):
      """
      A ImageField Widget that shows a thumbnail.
      """
  
      def __init__(self, attrs={}):
          super(ImageWidget, self).__init__(attrs)
  
      def render(self, name, value, attrs=None):
          output = super(ImageWidget, self).render(name, value, attrs)
          if value and hasattr(value, 'url'):
              output = ('<div class="val-wrap"><img src="%s" alt="" />%s</div>' %
                        (value.url, output))
          return output
  
new_contents: # Based on http://djangosnippets.org/snippets/1580/
  from django import forms
  
  
  class ImageWidget(forms.FileInput):
      """
      A ImageField Widget that shows a thumbnail.
      """
  
      def __init__(self, attrs={}):
          super(ImageWidget, self).__init__(attrs)
  
      def render(self, name, value, attrs=None, renderer=None):
          output = super(ImageWidget, self).render(name, value, attrs, renderer=renderer)
          if value and hasattr(value, 'url'):
              output = ('<div class="val-wrap"><img src="%s" alt="" />%s</div>' %
                        (value.url, output))
          return output
  
subject: Add required renderer argument to Widget.render() call