Lubuntu uses xscreensaver as it performs screensaver & lock functions, and does it rather lightly (as in isn’t wasteful on resources)
Every cycle or two someone asks on this site, on IRC, UF, AU or elsewhere on getting rid of the flame picture etc… which is something frowned upon by the creator & maintainer of the xscreensaver program. We’re free to use it, but not change their logo or the appearance of the app - so we don’t.
Maybe useful is other threads on this site, such as Replace xscreensaver, but if you look there are numerous.