Can be usefull for sniffer. 

def pixel_tracker(request):
    content = 'R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7'.decode('base64')
    response = HttpResponse(content, content_type='image/gif')
    response['Content-Length'] = len(content)
    return response