In earlier versions of Windows you had to use third party utilities to customize the login or lock screens. You could also accomplish it by editing the Windows Registry, but novice users don't want to go mucking about there.
With Windows 8 it is a much easier job. Click on the Control Panel tile to launch the Metro UI Control Panel.
Click on Personalize and you'll see a variety of options. Click on Browse to find an image file you want to use as the background for the lock screen, select it and click on Choose Picture to change it.
Presto! You now have a customized lock screen background.
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