Dlibの顔認証と画像貼り付け

Dlibを使った顔認証で、複数人の中から一人を選び顔貼り付けをしたいです

Pycharmでdlibを使って、webカメラを用いた顔検出を行なっています。（検出した顔の上に写真を貼り付けるプログラムになります。）
複数人の顔を認証し、全員に貼り付けするところまでできています。
どこを変えれば、特定の人物に貼り付けられるようになりますでしょうか？機械学習ではない方法で、何かあれば教えていてだきたいです。（貼り付けたい人物をクリックするとその人物にのみ貼り付けられるなど）
コードは下記の通りです。よろしくお願いします。


import cv2
import dlib
from datetime import datetime

IMAGE_PATH = "./niko.png"
CAPTURE_SCALE = 0.5

def main():

    detector = dlib.get_frontal_face_detector()
    predictor = dlib.shape_predictor("shape_predictor_68_face_landmarks.dat")

    cap = cv2.VideoCapture(0)

    while True:
        _, frame = cap.read()

        frame = img_resize(frame, CAPTURE_SCALE)
        h, w, _ = frame.shape

        img = frame
        dets = detector(frame[:, :, ::-1])

        if len(dets) > 0:
            parts = predictor(frame, dets[0]).parts()
            distance, pos = calc_distance_and_pos(img, parts)
            icon, icon_w, icon_h = load_icon(IMAGE_PATH, distance)

            if (pos != None) and (distance > 0.0):
                x = pos.x - int(icon_w / 2)
                y = pos.y - int(icon_h / 2)
                if (0 <= y) and (y <= (h - int(icon_h))) and (0 <= x) and (x <= (w - int(icon_w))):

                    img = merge_images(img, icon, x, y)

        cv2.imshow("camera", img)

        if len(dets) > 0:
            for det in dets:
                parts = predictor(frame, det).parts()
                distance, pos = calc_distance_and_pos(img, parts)
                icon, icon_w, icon_h = load_icon(IMAGE_PATH, distance)

                #if (pos != None) and (distance > 0.0):
                    #x = pos.x - int(icon_w / 2)
                    #y = pos.y - int(icon_h / 2)
                    #if (0 <= y) and (y <= (h - int(icon_h))) and (0 <= x) and (x <= (w - int(icon_w))):
                        #img = merge_images(img, icon, x, y)



        cv2.imshow("camera", img)

        k = cv2.waitKey(1) & 0xff
        if k == ord('q'):

            break
        elif k == ord('p'):

            save_image(img)
            cv2.imshow("saved", img)


    cap.release()
    cv2.destroyAllWindows()



def load_icon(path, distance):
    icon = cv2.imread(path, -1)
    icon_height, _ = icon.shape[:2]
    icon = img_resize(icon, float(distance * 1.5 / icon_height))
    icon_h, icon_w = icon.shape[:2]

    return icon, icon_w, icon_h



def img_resize(img, scale):
    h, w = img.shape[:2]
    img = cv2.resize(img, (int(w * scale), int(h * scale)))
    return img



def calc_distance_and_pos(img, parts):

    cnt = 0
    pos = None
    p1 = None
    distance = 0.0

    for i in parts:
        if (cnt == 0):

            p1 = i
        if (cnt == 16):

            distance = ((p1.x - i.x) ** 2 + (p1.y - i.y) ** 2) ** 0.5
        if (cnt == 33):
            pos = i
        cv2.putText(img, str(cnt), (i.x, i.y), cv2.FONT_HERSHEY_SIMPLEX, 0.3, (0, 0, 255), thickness=1,
                    lineType=cv2.LINE_8)
        cv2.circle(img, (i.x, i.y), 1, (255, 0, 0), -1)
        cnt = cnt + 1

    return distance, pos



def save_image(img):
    date = datetime.now().strftime("%Y%m%d_%H%M%S")
    path = "./" + date + ".png"
    cv2.imwrite(path, img)



def merge_images(bg, fg_alpha, s_x, s_y):
    alpha = fg_alpha[:, :, 3]
    alpha = cv2.cvtColor(alpha, cv2.COLOR_GRAY2BGR)
    alpha = alpha / 255.0

    fg = fg_alpha[:, :, :3]

    f_h, f_w, _ = fg.shape
    b_h, b_w, _ = bg.shape


    print("f_w:{} f_h:{} b_w:{} b_h:{} s({}, {})".format(f_w, f_h, b_w, b_h, s_x, s_y))

    bg[s_y:f_h + s_y, s_x:f_w + s_x] = (bg[s_y:f_h + s_y, s_x:f_w + s_x] * (1.0 - alpha)).astype(
        'uint8')
    bg[s_y:f_h + s_y, s_x:f_w + s_x] = (bg[s_y:f_h + s_y, s_x:f_w + s_x] + (fg * alpha)).astype('uint8')

    return bg

if __name__ == '__main__':
    main()