/usr/lib/libopencv_objdetect.so is in libopencv-objdetect-dev 2.3.1-7.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/libopencv_objdetect.so.2.3
/usr/lib/libopencv_objdetect.so.2.3