Das Gdm unterstützt bis zu 100 User bei der Anmeldung bei Ubuntu. Anbei das Use Cases das auf wiki.ubuntu.com veröffentlicht wurden ist.

Use Case

“The general advantage of a face-browser for login is the avoidance of superfluous typing. This helps speed up the login-procedure of all people, who are no touch-typists or experienced keyboard users. But even experienced users can enjoy the convenience of being lazy occasionally. It is still possible to login successfully without selecting an image at all just by typing in the login-name and password.

only one user on system: Although an automatic login would streamline the bootup-to-desktop cycle for a single-user system (single in terms of one real person, not “user” in terms of unix-privileges), security-concerns strongly advice against this. The single user will see only her/his photo in the face-browser.

multiple users on system (<=100): In this case a user can either just select her/his image to tell the computer their login-name or start typing the first few characters from her/his login-name and watch the face-browser filter the set of displayed images to fewer images in order to simplify locating their own image in the visible set of images.

multiple users on system (>100): Scalability-issues regarding texture-usage (especially on low-end graphics hardware) and network-latency (setups with that many users are hardly run of local harddisks) demand a fallback to a non-face-browser mode of the gdm-greeter. In that case plain text-entry widgets for login-name and password are used.

idle: When the computer is left running unattended without any user loggeded in, the gdm-greeter should switch to a screensaver-like display without locking input. Any motion of the mouse or pressed key should exit this mode. The screensaver-mode should use e.g. the user photos and make them fly round on the screen, but the user should always be able to identify that it is still the login-screen that is being displayed and not a normal screensaver from another users-session.

The threshold of a 100 users for automatic disabling the face-browser is something that needs to be properly tested during the beta-phase.”

Quelle: https://wiki.ubuntu.com/DesktopTeam/Specs/GdmFaceBrowser