def vflip(anns, size):
    """
    Vertically flip the bounding boxes of the given PIL Image.

    Parameters
    ----------
    anns : ``List[Dict]``
        Sequences of annotation of objects, containing `bbox` of [l, t, w, h].
    size : ``Sequence[int]``
        Size of the original image.
    """
    w, h = size
    new_anns = []
    for ann in anns:
        bbox = list(ann['bbox'])
        bbox[1] = h - (bbox[1] + bbox[3])
        new_anns.append({**ann, "bbox": bbox})
    return new_anns