This is the exact error that I am getting. My OS is Ubuntu 16.10.
OpenCV Error: Unspecified error (The function is not implemented. Rebuild the library with
My Envirment is Win10, and I added the anaconda path to the environment variables's PATH’,the cv2.imshow worked
C:\Users\user\Anaconda3 C:\Users\user\Anaconda3\Scripts
Then restart the windows