Hi,
before version 25, it was possible to customize LibreOffice with other options, an there was also an old legacy with personas which let you use a picture as background for main interface.
Rather than speaking, this is what I currently have on another PC with version 24 :
http://darkwolflair.free.fr/films/LibreOffice24.png
It seems that this kind of option may come back in a near future, but I just want to have some news about this feature, if it has been scheduled or not (I really love setting up my LO with these kind of pictures).