warning: libopencv_core.so.4.2, needed by /opt/ros/foxy/lib/libcv_bridge.so

原因：ros用的opencv版本与自己安装的opencv版本不同

解决方案：https://www.cnblogs.com/iamheying/p/17028586.html

git clone https://github.com/ros-perception/vision_opencv.git -b foxy

cd vision_opencv/cv_bridge
mkdir build && cd build
cmake -DCMAKE_INSTALL_PREFIX=/opt/ros/foxy ..
sudo make install