You should be using the {{ MEDIA_URL }}
tag in your templates, which you define in settings.py.
Example in settings.py:
MEDIA_URL = '/media/'
MEDIA_ROOT, like STATIC_ROOT, is the directory that Django uses to upload media files to and serve media files from, not the URL path.
See: https://docs.djangoproject.com/en/dev/howto/static-files/#serving-files-uploaded-by-a-user