Screensaver Lockscreen and Background GPO

Idle lock screen timeout settings:

Computer Configuration > Policies > Windows Settings > Security Settings > Local Policies > Security Options

• Interactive logon: Machine inactivity limit
  • Enable
  • Set timeout in seconds.

Force a specific Background:

User Configuration > Policies > Administrative Templates > Desktop > Desktop

• Desktop Wallpaper
  • Enable
  • Set a UNC path to the wallpaper ( i.e. \\path\to\file.jpg )