code：

import cv2
img = cv2.imread("D:\123.jpg")
cv2.namedWindow("Image")
cv2.imshow("Image", img)
cv2.waitKey(0)
cv2.destroyAllWindows()

OpenCV Error: Assertion failed (size.width>0 && size.height>0) in cv::imshow, file ..\..\..\opencv-3.1.0\modules\highgui\src\window.cpp, line 289
Traceback (most recent call last):
  File "C:/Users/zyj/untitled6/opencv.py", line 5, in <module>
    cv2.imshow("Image", img)
cv2.error: ..\..\..\opencv-3.1.0\modules\highgui\src\window.cpp:289: error: (-215) size.width>0 && size.height>0 in function cv::imshow

解決辦法：

將圖片路徑，即程式碼第二行 

img = cv2.imread("D:\123.jpg")

img = cv2.imread("D:\\123.jpg")    #兩個斜槓