In full screen, I expect to only see on single image, instead of being encumbered with the meta-information tag bar. I know I can move the thing to the side, but it turns back on again when I open a new picture.

How can I disable the meta information bar in Gwenview 15.12.3?

Just hit the F4, the sidebar is gone. Hit again to reappear

Thanks! Didn't realise it was just a shortcut key away.