The Login Window in OS X is the screen you see while you’re typing in a username and password. There are a number of customizations used in some environments to make the system easier for users to use, or to make it more specific to a given user environment. One such is customizing the Login Window’s background, which can be done by replacing this file with one that you would like to use: /System/Library/PrivateFrameworks/LoginUIKit.framework/Versions/A/Frameworks/LoginUICore.framework/Versions/A/Resources/appleLinen.png You can also configure a message to be shown to users. This message, often referred to as an Acceptable Use Policy, can be used as a policy banner that users must accept in order to log…