It looks like digiKam installed on a default Gnome environment has missing icons. For example the "pick" icons (the little flags for Rejected/Pending/Accepted) are missing. The reason is that the default Gnome icon pack, Adwaita is missing some of the icons used by digiKam.
The solution is to install the Breeze icon theme and then select it in digiKam:
$ sudo apt install breeze-icon-theme
and then in digikam Settings -> Configure digiKam -> Miscellaneous -> Appearance -> Icon theme and select "Breeze". Actually you can leave it as "Use Icon Theme From System" and it will use Adwaita and only fall back to Breeze for missing icons. However, I do find it more pleasant to have a consistent icon theme.
thanks – that was really bugging me.
is there a way to change the right hand tool panel to show as a list (same look as under tool menu) rather than as icon layout with text underneath which looks messy?
Awesome, thanks for the info, saved me a lot of time!!