If you share a Windows 8 PC with others and don’t want them messing with the lock screen image, you can lock it so that it can’t be changed. To do it, though, you’re going to have to get down and dirty by editing the Registry.
When you’re on the Start screen, type REGEDIT, click Apps on the right-hand side of the screen, then click the regedit.exe icon that appears on the left side of the screen.
A security window appears asking if you want to allow the Registry Editor to make changes to your PC. Click Yes, and the Registry Editor launches.
See if there’s a key called Personalization there. If the key already exists, don’t create another one. Instead, follow the instructions in the next paragraph. If the key doesn’t exist, you’ll have to create it. To do so, click Edit –> New –> Key. That creates a new key, but it will have a name like “New Key #1.” You have to rename it. Right-click it, select Rename, and rename it Personalization.
Now that the Personalization key is there, create a new DWORD value under it called NoChangingLockScreen. To do that, right-click the Personalization key and select New –> DWORD (32-bit) Value. Rename the DWORD value NoChangingLockScreen. Double click-it and change its value from 0 to 1. Exit the Registry Editor.
Log out of Windows or restart it, then log back in. The lock screen background shouldn’t be changeable — consider it locked. If you want to allow the background to be changed in the future, use the Registry Editor to change the value of NoChangingLockScreen from 1 to 0.
Please Note: Before performing these tweaks, we recommend backing up your systems registry. To back up the Registry the easy way, simply open Control Panel, click System, and then click System protection on the left sidebar. Click the big Create button to have Windows walk you through the straightforward process of creating a System Restore Point — it’s as easy as that.