Trying a different route with
http://scanthis.net/which uses
ScanThis is powered by the open source and industry-recognised Clam AV software.
because the file info is not informative at all to me . There is no .exe in it just for starters.
Since the file in question is entrance.jpg.
I am only uploading that one to be scanned presently.
It is still scanning as I type this post out. So will wait to see what is what for sure.
That injected code the other site showed was just jumbled html code which I cannot decipher.
Sure is taking a long long time to scan one .jpg. Must be a zillion virus signatures to look for I guess.

Ok. Got tired of waiting so went to
https://www.metascan-online.com/#!/results/file/c15d48726a80498490d8b8b1e8cfe6da/regular
So my uneducated conclusion is that entrance.jpg in /usr/share/backgrounds/xfce/entrance.jpg is tainted somehow since double checked on another site and I am going to delete it of all my boxes/installs.
It can't hurt to do so. Plus. If you look at my screenshots. I never use the default stuff anyways.
Up to the team to decide where to take this from here. I can only speak for myself.
Because. Even after all that. You still get
Only a few scan engines detected this file as a threat. If you think it might be a false positive, find out how to contact the engine vendor on our blog
Edit> I am closing the scan this tab open right now. It is still not done scanning and my patience aint what it used to be.