User Configuration > Administrative Templates > Microsoft PowerPoint 2016 > PowerPoint Options > Security
User
HKCU\software\policies\microsoft\office\16.0\powerpoint\security
This policy setting determines whether PowerPoint automatically downloads links from external sources. If you enable this policy setting, PowerPoint will load images saved in remote locations. If you disable or do not configure this policy setting, when PowerPoint opens a presentation it does not display any linked images saved on a different computer unless the presentation itself is saved in a trusted location (as configured in the Trust Center).