The entry "Guest Session" and the Ubuntu logo are barely visible when a bright wallpaper is selected.

[Andrea Virgillito]

The entry "Guest Session" and the Ubuntu logo are barely visible when a bright wallpaper is selected.
These elements need a darker background for a better accessibility.

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Robert Ancell (robert-ancell)]

Need design input on what to do in these cases. Note you can run unity-greeter in a test mode with the following from a terminal:
$ unity-greeter --test
In this mode there is a list of fake users that test the different cases in the greeter. See "Black Background" and "White Background" to see how the greeter behaves with dark and light backgrounds.

[Robert Ancell (robert-ancell)]

That should be:
 $ unity-greeter --test-mode

[Mo-Yu Mandy Zhou (zhou-mandy)]

The username on the top left is also difficult to read. On light gray wallpapers it practically blends into the top bar. I submitted this as part of a bug (Bug #1042417) but it was just marked as a duplicate of this one. Shouldn't be too hard to fix; the time on the top right of the screen is much more readable, so if the formatting of the username is made to match that of the time, it should look much better.

As for the readability of 'Guest Session' and the logo, perhaps you could put a shadow behind those to make them stand out from a light background.