def source_url(farm, server, id, secret, size):
    """url for direct jpg use"""
    if size == 'small':
        img_size = 'n'
    elif size == 'medium':
        img_size = 'c'
    elif size == 'large':
        img_size = 'b'
    return 'https://farm{}.staticflickr.com/{}/{}_{}_{}.jpg'.format(farm,
        server, id, secret, img_size)
