Pillow returns the error : "IOError: image file is truncated (6 bytes not processed)"

I use Pillow 4.1.1 with Python 2.7 / Django 1.9

I have dozens of thousands of user-uploaded pictures on my website and I use pillow to generate thumbnails from the templates.

E.g.:

{% thumbnail apicture.file "1200x350" crop="center" as im %}
    <img src="{{ im.url }}" width=100%>
{% endthumbnail %}

It was working very well until this week. Django now shows this error:

IOError: image file is truncated (6 bytes not processed)

Solutions found on stackoverflow do not work, as they all apply to views and not templates (e.g. ImageFile.LOAD_TRUNCATED_IMAGES = True).

Is there a simple way to identify which pictures generate this error ? How to solve this bug ?

Here is the full traceback:

Internal Server Error: /trip/province-dublin-2034
Traceback (most recent call last):
  File "C:\Python27\lib\site-packages\django\core\handlers\base.py", line 149, in get_response
    response = self.process_exception_by_middleware(e, request)
  File "C:\Python27\lib\site-packages\django\core\handlers\base.py", line 147, in get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)    
  File "C:\Terradiem\terradiem\trip\views.py", line 300, in trip
    return render(request, 'trip/results.html', qsall)
  File "C:\Python27\lib\site-packages\django\shortcuts.py", line 67, in render template_name, context, request=request, using=using)
  File "C:\Python27\lib\site-packages\django\template\loader.py", line 97, in render_to_string
    return template.render(context, request)
  File "C:\Python27\lib\site-packages\django\template\backends\django.py", line 95, in render
    return self.template.render(context)
  File "C:\Python27\lib\site-packages\django\template\base.py", line 206, in render
    return self._render(context)
  File "C:\Python27\lib\site-packages\django\test\utils.py", line 92, in instrumented_test_render
    return self.nodelist.render(context)
  File "C:\Python27\lib\site-packages\django\template\base.py", line 992, in render
    bit = node.render_annotated(context)
  File "C:\Python27\lib\site-packages\django\template\base.py", line 959, in render_annotated
    return self.render(context)
  File "C:\Python27\lib\site-packages\django\template\defaulttags.py", line 220, in render
    nodelist.append(node.render_annotated(context))
  File "C:\Python27\lib\site-packages\django\template\base.py", line 959, in render_annotated
    return self.render(context)
  File "C:\Python27\lib\site-packages\django\template\defaulttags.py", line 220, in render
    nodelist.append(node.render_annotated(context))
  File "C:\Python27\lib\site-packages\django\template\base.py", line 959, in render_annotated
    return self.render(context)
  File "C:\Python27\lib\site-packages\django\template\defaulttags.py", line 326, in render
    return nodelist.render(context)
  File "C:\Python27\lib\site-packages\django\template\base.py", line 992, in render
    bit = node.render_annotated(context)
  File "C:\Python27\lib\site-packages\django\template\base.py", line 959, in render_annotated
    return self.render(context)
  File "C:\Python27\lib\site-packages\sorl\thumbnail\templatetags\thumbnail.py", line 59, in render
    return self._render(context)
  File "C:\Python27\lib\site-packages\sorl\thumbnail\templatetags\thumbnail.py", line 137, in _render
    thumbnail = get_thumbnail(file_, geometry, **options)
  File "C:\Python27\lib\site-packages\sorl\thumbnail\shortcuts.py", line 8, in get_thumbnail
    return default.backend.get_thumbnail(file_, geometry_string, **options)
  File "C:\Python27\lib\site-packages\sorl\thumbnail\base.py", line 125, in get_thumbnail
    thumbnail)
  File "C:\Python27\lib\site-packages\sorl\thumbnail\base.py", line 157, in _create_thumbnail
    image = default.engine.create(source_image, geometry, options)
  File "C:\Python27\lib\site-packages\sorl\thumbnail\engines\base.py", line 21, in create
    image = self.colorspace(image, geometry, options)
  File "C:\Python27\lib\site-packages\sorl\thumbnail\engines\base.py", line 53, in colorspace
    return self._colorspace(image, colorspace)
  File "C:\Python27\lib\site-packages\sorl\thumbnail\engines\pil_engine.py", line 101, in _colorspace
    return image.convert('RGB')
  File "C:\Python27\lib\site-packages\PIL\Image.py", line 844, in convert
self.load()
  File "C:\Python27\lib\site-packages\PIL\ImageFile.py", line 226, in load
"(%d bytes not processed)" % len(b))
IOError: image file is truncated (6 bytes not processed)

Thank you