The default picture viewer on Xubuntu's XFCE is risterroro. Risterroro is quite lightweight, but anyways is lacking even basic functionality with reading a number of pictures in a directory and showing, them one by one lacks any picture automated slider. The lack of picture back/forward functionality makes picture viewing very inconvenient on those Linux distro.
Thanksfully this kind of unconfortable default behaviour on Xubuntu can easily be changed to use a handy picture viewer program called gpicview
xubuntu-linux:~# apt-get install --yes gpicview
Gpicview is a good minimalistic program which has all the functionality of the default GNOME picture viewer program eog – (eye of the Gnome). If you're aaccustomed to GNOME's eog you can always install and use eog instead 🙂