pythonのopencvのエラーについて

以下の記事をもとにダウンロードしたプログラムがエラーを吐いています
記事
プログラムはこちらです

import apple_keras as apple
import sys, os
import numpy as np
import subprocess
import cv2
from keras.preprocessing.image import load_img, img_to_array

cam = cv2.VideoCapture(0)
image_size = 32
categories = ["赤りんご", "青りんご"]

def main():

    def jtalk(t):
        open_jtalk=['open_jtalk']
        mech=['-x','/var/lib/mecab/dic/open-jtalk/naist-jdic']
        htsvoice=['-m','/usr/share/hts-voice/mei/mei_happy.htsvoice']
        speed=['-r','1.0']
        outwav=['-ow','open_jtalk.wav']
        cmd=open_jtalk+mech+htsvoice+speed+outwav
        c = subprocess.Popen(cmd,stdin=subprocess.PIPE)
        c.stdin.write(t)
        c.stdin.close()
        c.wait()
        aplay = ['aplay','-q','open_jtalk.wav']
        wr = subprocess.Popen(aplay)

    while(True):
        ret, frame = cam.read()
        cv2.imshow("Show FLAME Image", frame)

        k = cv2.waitKey(1)
        if k == ord('s'):
            cv2.imwrite("output.png", frame)
            cv2.imread("output.png")

            X = []
            img = load_img("./output.png", target_size=(image_size,image_size))
            in_data = img_to_array(img)
            X.append(in_data)
            X = np.array(X)
            X  = X.astype("float")  / 256

            model = apple.build_model(X.shape[1:])
            model.load_weights("./image/apple-model.h5")

            pre = model.predict(X)
            print(pre)
            if pre[0][0] > 0.9:
                print(categories[0])
                text = 'これは' + categories[0]+ 'だよ'
                text = text.encode('utf-8')
                jtalk(text)
            elif pre[0][1] > 0.9:
                print(categories[1])
                text = 'これは' + categories[1]+ 'だよ'
                text = text.encode('utf-8')
                jtalk(text)

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

    cam.release()
    cv2.destroyAllWindows()

if __name__ == '__main__':
    main()

これで出たエラーはこちらです

Using TensorFlow backend.
OpenCV: error in [AVCaptureDeviceInput initWithDevice:error:]
2019-06-13 22:03:29.350 python[50712:5707123] OpenCV: Cannot use FaceTime HD Camera
OpenCV: camera failed to properly initialize!
Traceback (most recent call last):
  File "apple_checker_cv.py", line 67, in <module>
    main()
  File "apple_checker_cv.py", line 30, in main
    cv2.imshow("Show FLAME Image", frame)
cv2.error: OpenCV(4.0.0) /Users/travis/build/skvark/opencv-python/opencv/modules/highgui/src/window.cpp:350: error: (-215:Assertion failed) size.width>0 && size.height>0 in function 'imshow'

おそらくopencv関連だと思いますが全くわかりません。
よろしく願いします