My lock screen changed one day from the default:

to this different one:

I am running Ubuntu 14.10. The install was originally a 14.04 that I upgraded to 14.10. The lock screen did not change at that point. Since then, I've just simply been periodically installing updates and adding software packages here and there. I'm not positive but I think the lock screen changed after I installed some packages from the Ubuntu repos (might have been MuseScore) using apt-get.
This is not a big deal, but I wish I knew why it randomly changed . Any idea why it did this?
Edit: Here is the output of dpkg --get-selections | -v deinstall, as requested by Tim.
