/usr/include/opencv2/stitching/detail/ is in libopencv-stitching-dev 3.2.0+dfsg-4build2.
This file is owned by root:root, with mode 0o755.
..
/usr/include/opencv2/stitching/detail/autocalib.hpp
/usr/include/opencv2/stitching/detail/blenders.hpp
/usr/include/opencv2/stitching/detail/camera.hpp
/usr/include/opencv2/stitching/detail/exposure_compensate.hpp
/usr/include/opencv2/stitching/detail/matchers.hpp
/usr/include/opencv2/stitching/detail/motion_estimators.hpp
/usr/include/opencv2/stitching/detail/seam_finders.hpp
/usr/include/opencv2/stitching/detail/timelapsers.hpp
/usr/include/opencv2/stitching/detail/util.hpp
/usr/include/opencv2/stitching/detail/util_inl.hpp
/usr/include/opencv2/stitching/detail/warpers.hpp
/usr/include/opencv2/stitching/detail/warpers_inl.hpp