def crop(img, box):
    """
    Crop regoin of box in image.
    Input:
        img: np.array
        box: (left, top, width, height), int
    Return:
        croped_img: np.array    
    """
    croped_img = img[box[1]:(box[1]+box[3]), box[0]:(box[0]+box[2])]
    return croped_img