As you know, before 1607, the lock screen and login screen were different, and now in 1607 they have been unified with the same background.
Except it hasn't on one of my machines. Now the lock screen is black (with text on it, like that "Do you like what you see?" question), and only when I tap the spacebar to get the login prompt, then the background picture pops up. And it's not a gradual fade-in. It pops up immediately. So for some reason, that picture doesn't seem to be registering on the lock screen. IOW, it seems the two screens are still somewhat independent from each other in Win 10. MS cosmetically "unified" them by having them share the same background, except that background is missing on my lock screen.
And what's worse, MS has blocked deactivation of the lock screen, which for me is useless anyway.