Once you have finished editing your file save it in your directory:WoWInterfaceLoginScreenand name it:Background.pngNow all you have to do is drag and drop the .png file onto your BLP Converterand remove the .png file out of the directory.
you are not confused you are noob one of firsts Rules of WoW editing is that every Image in WoW need to haev mirrored Resolition2x24x48x816x1632x3264x64128x128256x256512x5121024x10242048x2048etc
Is this also working on 2.4.3 (TBC) Clients? Cause i always get error when starting WoW after adding new patch file.