Install DLib machine learning library

Download Visual Studio 2019 Community Edition from 
https://visualstudio.microsoft.com/vs/

and choose "Python development" and "Desktop development with C++"

Then run
pip install dlib

OR

download dlib source code and run the command inside its folder
python setup.py install 

OR

install  miniconda, then run the next command 

conda install -c conda-forge dlib