/usr/lib/x86_64-linux-gnu/libpng12.so is in libpng12-dev 1.2.46-3ubuntu4.
This file is owned by root:root, with mode 0o777.
It is a symlink to /lib/x86_64-linux-gnu/libpng12.so.0
/lib/x86_64-linux-gnu/libpng12.so.0