/usr/share/doc/libopencv-calib3d2.3/changelog.Debian.gz is in libopencv-calib3d2.3 2.3.1-7.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/doc/libopencv-calib3d2.3/../libopencv-core2.3/changelog.Debian.gz