fatal error: 'opencv2/core/version.hpp' file not found

micchang002gmail.com@MacBook-Pro darknet % make chmod +x *.sh g++ -std=c++11 -std=c++11 -Iinclude/ -I3rdparty/stb/include -DOPENCV pkg-config --cflags opencv4 2> /dev/null || pkg-config --cflags opencv -Wall -Wfatal-errors -Wno-unused-result -Wno-unknown-pragmas -fPIC -Ofast -DOPENCV -c ./src/image_opencv.cpp -o obj/image_opencv.o /bin/sh: pkg-config: command not found ./src/image_opencv.cpp:16:10: fatal error: 'opencv2/core/version.hpp' file not found #include <opencv2/core/version.hpp> ^~~~~~~~~~~~~~~~~~~~~~~~~~ 1 error generated. make: *** [obj/image_opencv.o] Error 1 micchang002gmail.com@MacBook-Pro darknet %