LXDE wallpaper with dual monitor
I connected an external screen to my laptop and installed lxde.
The first time I used it, in the wall paper settings, setting background colour as black without wallpaper worked on the external monitor, but not the internal one. I created a black picture, did set it as wallpaper streched and it worked.
However, after reboot, the wall paper was only on one monitor (external one) and on the laptop screen it is the default lxde blue wallpaper (plus the trash icon that is configured not to be displayed).
Now, changing the desktop preferences apparently only affects the external monitor, not the laptop monitor. In the desktop preference graphical menu, in the menu for the wallpaper display mode, the first choice is "strech to fill the entire screen" and so is the last choice (I am using French, not sure whether it is a translation issue). Choosing the first choice makes the wallpaper stretch over the external display, choosing the last choice makes it stretch more as if to cover both monitors, while in both cases the internal monitor keeps the default lxde blue wallpaper.