/usr/share/doc/debian-edu-doc-nb/debian-edu-jessie-manual-images/alert.png is in debian-edu-doc-nb 1.6~20170429+deb8u4.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/doc/debian-edu-doc-nb/debian-edu-jessie-manual-images/../../debian-edu-doc-en/debian-edu-jessie-manual-images/alert.png