why can't I change the gnome login-screen logo?

Question

From the dconf-editor I find that the logo shown in login-screen can be changed,so I made some logoes which are the same size and same type of the original logo（even more,I make sure they have the same permission as the original one）.And I put these logoes in the (just like the original one),then change the setting by dconf-editor to show my logo on login-screen. （与原始徽标相同），然后通过dconf-editor更改设置以在登录屏幕上显示我的徽标。

But,it does not work! I have tried log out and log in,restart my pc,still does not work.The login-screen still show the old logo .

ps:this is my environment:
gnome-session:GNOME Shell 3.10.4
ubuntu：3.13.0-48-generic

Anyone could help?
thx a lot!

Answer 1

要应用更改：

 sudo update-initramfs -u