[Answered ]-Django reads images without defining MEDIA_URL

No images should not be viewable if you remove

MEDIA_URL = '/media/'
MEDIA_ROOT = os.path.join(BASE_DIR, 'media')

from settings.py

and

+ static(settings.MEDIA_URL, document_root=settings.MEDIA_ROOT)

If they are, it is probably just because your browser cached the images.

Try doing CNTL + SHIFT + DEL while in your browser and clearing the cache. Then reload your django web page.