How can I customize the Lion login screen to remove the vignette effect? Just upgraded to Lion, but the new login screen needs some colour. I found someone online who posted the address of the image that's in the background, so I went and replaced that.  

Only, after doing that, I realized that there's an additional overlay being drawn that adds a vignette effect by brightening the center of the screen. 

Does anyone know of a way to remove this?
I suspect that the effect is actually something that's drawn programmatically. I dug around for a while and I can't seem to find it anywhere. My suggestion: Open your image in a graphics editor and modify it to account for the shadow.