checking for OPENCV... no
configure: error: Package requirements (opencv >= 3.0) were not met:

Package 'opencv', required by 'virtual:world', not found

Consider adjusting the PKG_CONFIG_PATH environment variable if you
installed software in a non-standard prefix.

Alternatively, you may set the environment variables OPENCV_CFLAGS
and OPENCV_LIBS to avoid the need to call pkg-config.
See the pkg-config man page for more details.