def save_image_in_field(modelfield, url='',relativefile='',filename=None):
    ''' Takes a model field of that model and a optional url or a filename
    and saves the image to that field. 
    The url must be absolute
    The filename is relative to the firsr static dir, using Unix style slashes /
    The field must be a DjangoImageField'''

    if url and relativefile:
        raise UserWarning('Function save_image_in_field expects a URL or a Filename not both.')
        
    if not filename:
        filename = url.split('/')[-1]
        
    if url:
        r = requests.get(url)
        data = r.content
        
    if relativefile:
        r = open(os.path.join(settings.MEDIA_ROOT,filename),'rb')
        data = r.read()
        
    img_temp = NamedTemporaryFile(delete=True)
    img_temp.write(data)
    img_temp.flush()
        
    modelfield.save(filename, File(img_temp), save=True)