Another new feature found in Windows 8, by tweaking user’s theme file you can use your desktop background as lockscreen (appears when you lock your system). You can try this with the current Windows 8 build 7955 .
Enable Windows 8 Login Screen Background to use Desktop wallpaper
1. Open C:\Windows\Resources\Ease of Access\basic theme in Notepad
2. Change “SetLogonBackground” value from ‘0’ to ‘1’.
3. Restart your Computer.
From now onwards you’ll have unique desktop background appears on lockscreen when you lock your system. You can use Ctrl+Alt+Del shortcut enter into Windows by entering password.