raspberry camera module cannot be opened with device ID

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i am trying to run this face recognition code that i have got from here.

i successfully installed OpenCV on the raspberry, and i used the code before on windows.

but here i have the problem with the raspberry camera module device ID, i tried the values 0-9 values for the ID , The Capture Device ID 0 cannot be opened. is all i get.

any help would be great. thank you