Check out example codes for "ModuleNotFoundError: No module named 'cv2'". It will help you in understanding the concepts better.

Code Example 1

To solve this run the following
# main opencv
pip install opencv-python
# contrib package for the extra features
pip install opencv-contrib-python

The official installation instructions are on the opencv website.
More info can be found here: 
https://www.pyimagesearch.com/opencv-tutorials-resources-guides/

Code Example 2

python -m pip install opencv-python

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