How can I change the lock screen background image in Lion 10.7.4?

With Lion, I know that, in order to change the lock screen background image, I have to change

/System/Library/Frameworks/AppKit.framework/Versions/C/Resources/NSTexturedFullScreenBackgroundColor.png

In particular, I used an image with the same size as the resolution of my MacBook screen (1440x900).

So far so good, but after the update to Lion 10.7.4, the lock screen background switched back to the gray texture. I thought that the upgrade overwrote my custom image, but it didn't. I tried overwriting my image, but again, nothing changed.
Now I'm stuck with that dull texture. Can someone help me please?

Note: Please note that I'm not trying to change the login screen background, there are plenty of answers related to that problem.

/System/Library/PrivateFrameworks/LoginUIKit.framework/Versions/A/Frameworks/Log inUICore.framework/Versions/A/Resources/appleLinen.png

This is the new location to change the login screen wallpaper but im still figuring out how to put it to the fullscreen.