installation steps:
Install opencv3.4.5 under ubuntu16.04 (super detailed) https://blog.csdn.net/Ding_0110M/article/details/88083741
Installation of OpenCV under Ubuntu (with face detection demo) https://www.linuxidc.com/Linux/2016-07/132879.htm
Coexistence of multiple versions:
ubuntu installs OpenCV3 after installing OpenCV4, and multiple versions coexist https://blog.csdn.net/wyyang2/article/details/103989455
View version:
pkg-config --modversion opencv4
pkg-config --cflags opencv4
pkg-config --libs opencv4
Compile the samples source code that comes with opencv:
https://blog.csdn.net/Wuzebiao2016/article/details/79252731