escapejs
Escapes characters for use in JavaScript strings. This does not make the string safe for use in HTML, but does protect you from syntax errors when using templates to generate JavaScript/JSON.
<img class="profilfoto" src="{{MEDIA_URL|escapejs}}{{user.foto.name}}" />
Your above code results to, for example: user/2013\u002D04\u002D10_170411/image.png
, which giving you 404 error while loading this image.
UPDATE:
when you save or update an image, you must define the enctype in the form. This will allow you to save an image or a file:
<form id="registerform" action="/angemeldet/" method="post"
enctype="multipart/form-data">
{% csrf_token %}
AND
form = YourForm(request.POST, request.FILES)
if form.is_valid():