The "noise texture" that is used to stipple the background of the login and
lock screens is optimally bad for remote desktop.  It successfully defeats
almost any compression system used by remote desktop viewers.

In earlier versions, this existed as a stand-alone file that could be moved
aside with dpkg-divert.  In 3.16, however, it is now baked into
/usr/share/gnome-shell/gnome-shell-theme.gresource along with many other
items and can't seemingly be changed.