/usr/share/psychtoolbox-3/PsychTests/konijntjes1024x768gray.jpg is in psychtoolbox-3-common 3.0.14.20170103+git6-g605ff5c.dfsg1-1build1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/psychtoolbox-3/PsychTests/../PsychDemos/konijntjes1024x768gray.jpg