use yolo3 to detectar face in image and count Number of people in image

def detect_face(img):

    # create copy of the image
    img_cp = img.copy()

    # create a blob from the image
    blob = cv2.dnn.blobFromImage(img_cp, 1 / 255.0, (416, 416),
                                 swapRB=True, crop=False)

    # set the blob as the input to the network
    net.setInput(blob)

    # run inference through the network and gather predictions from output layers
    layer_names = net.getLayerNames()
    output_layers = [layer_names[i[0] - 1] for i in net.getUnconnectedOutLayers()]
    outs = net.forward(output_layers)

    # initialization
    class_ids = []
    confidences = []
    boxes = []
    conf_threshold = 0.5
    nms_threshold = 0.4

    # for each detetion from each output layer 
    # get the confidence, class id, bounding box params
    # and ignore weak detections (