Debian Multimedia :: Images Of All Kinds Missing

I have a problem with my Debian 8 installation. This morning I was playing around with libvirt and virt-manager while I was routinely installing updates using apt-get. While doing that, my system crashed (probably because of the running Win8 VM). After resetting (in hardware), I got access to the emergency console where I tried executing "dpkg --configure -a" which worked.

After restarting, I first noticed that the login screen background (just the normal Jessie one on LXDM) was missing and the screen was black instead. After logging in, I saw that nearly every image/icon/whatever is missing. For example:

- the icons in lxpanel (I use LXDE)
- the copy and paste icons nearly everywhere
- the New Tab icon in Firefox
- many more icons
- the desktop and login background

A few images are still there:
- interestingly, the lxpanel icons are replaced by "icon missing" icons which still work
- most icons in Firefox except for New Tab
- all images of LibreOffices (so this problem might be Gtk+ only)

Some programs don't work (obviously because they can't load their menu icons and don't a fallback). An example for this would be Inkscape. It crashes at start:

Code: Select all(inkscape:2513): Gtk-WARNING **: Error loading theme icon 'document-open' for stock: Format der Bilddatei unbekannt
(inkscape:2513): Gtk-WARNING **: Error loading theme icon 'document-open' for stock: Format der Bilddatei unbekannt
(inkscape:2513): Gtk-WARNING **: Error loading theme icon 'document-open' for stock: Format der Bilddatei unbekannt

[Code] .....

Note: I use a German system. "Format der Bilddatei unbekannt" means something like "Format of image file is unknown", "Bildtyp 'xpm' wird nicht unterstützt" means "xpm image type is not supported".

Concerning the desktop background, I looked at /etc/alternatives/desktop-background and found a correct SVG image which was the one I had before.

How I could restore these images?