While Digikam needs a database, it comes bundled with showPhoto (I have v 4.0.0beta3 right now, don't know if showPhoto was available in earlier Versions).
showPhoto is a standalone image viewer, without database. It displays pretty much the same metadata as Digikam does.
This is a good option for someone who needs both: indepth asset management and a quick viewer with editing features...
Personally I can recommend Gwenview, too. Metadata display can be fully customized and it displays every kind of data.
eog) is also the default image viewer in Lubuntu. It can display some, but not all, metadata in a side panel, not needing a second window. Choose "View → Side Pane" or, in fullscreen mode, pressCtrl + F9to see it. – tanius Dec 31 '17 at 14:29