Here's how I changed it on the first day when RTM came out in august:
- You need to go here: "C:\ProgramData\Microsoft\Windows\SystemData\S-1-5-18\ReadOnly\LockScreen_Z" (you'll need to make yourself owner and make full access permissions to all subfolders to access this folder)
- You'll find there a file called "LockScreen___RESX_RESY_notdimmed.jpg" image. (RESX is you horizontal resolution, RESY is your vertical resolution.) (little extra info: when RTM came out, the "notdimmed" word was not in the filename, some windows update made that there.)
- You need to set yourself owner and full access permission on this file too, then rename it to "LockScreen___RESX_RESY_notdimmed.jpg.bak"
- Then you'll need an image which has the same resolution as your screen resolution. Rename your image to "LockScreen___RESX_RESY_notdimmed.jpg" (RESX is you horizontal resolution, RESY is your vertical resolution.) and copy it to this folder.
- Then you need to set at least "read" permission for "System" user for this new image file.
- You are done!
(Once I needed to redone this, after that "notdimmed" windowsupdate came out, but other than that it works perfectly.)