def passes_min_size(trajectory, min_face_size):
    """Check that faces have a certain minimum (pixel) size. This is useful if
    we want to have reliable embedddings of images in a trajectory.
    """
    for bbs in trajectory["bbs"]:
        # Bounding boxes (bbs) are: x1, y1, x2, y2
        w, h = (bbs[2] - bbs[0]), (bbs[3] - bbs[1])
        if min(w, h) < min_face_size:
            return False
    return True