/usr/lib/x86_64-linux-gnu/libpng16.so is in libpng16-dev 1.6.20-2.
This file is owned by root:root, with mode 0o777.
It is a symlink to /lib/x86_64-linux-gnu/libpng16.so.16
/lib/x86_64-linux-gnu/libpng16.so.16