def validate_resize_factor(factor):
    """Validates resizing/scaling factor argument.

    Parameters
    ----------
    factor : float
        A factor by which the images or the bounding box annotations should be scaled.

    Returns
    ----------
    None

    Raises
    ----------
    ValueError
        When `factor` is not positive.
    """
    if factor <= 0:
        raise ValueError(
            'Resize factor must be positive. The value provided was {}'.
            format(factor))
