cv2.imwrite function not working via php server

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My Problem:- I am calling python opencv program for image detection via php file or on php server.In that files all works good but cv2.imwrite function does't working properly and does't write or save any image in my any directory (current working or desire location directory). I also tried python predefined image save function but it does't work.I notice a error in python file that when I run that same file at terminal then cv2.imwrite function returns "True" and save or write image in my directory but when same thing I run via php file using shell_exec or exec function then it returns me "False" nothing will save or write in my directory.

What actually I want to do:- Whatever camera capture images or provided by us then that detected face images send to my localhost directory or server directory via php.