Change the Default Lock Screen Image in Windows 8
With the November 2012 cumulative update, Microsoft included a new feature for Windows 8 Pro and Windows 8 Enterprise Edition that allows users to customize the default lock screen. Best of all the change is made using group policies which means you can easily deploy it across all Windows 8 machines on a domain. If you do not have a domain you can still use local group policies to apply the change. This is very useful if
you want to brand your computers with a company logo or are simply tired of looking at the default lock screen.
To get started you will need to make sure you have the November 2012 cumulative update installed KB2770917. The instructions below are for local group policy but they can also be easily adapted for a domain group policy.
Open the Start Screen and type in gpedit.msc and hit Enter.
When the Local Group Policy Editor loads, navigate through Local Computer Policy, Computer Configuration, Administrative Temples, Control Panel and then Personalization.
Right click on Force a specific default lock screen image and select Edit.
Select Enabled and provide a path to a JPG file that you want to you. You can use a local directory path or even a UNC network share.
Click OK and reboot your computer.