Thanks to Windows 7’s built-in feature for OEM manufactures customizing their products, WITHOUT the help of any software/program, one is allowed in principle to change his favorite JPEG as the logon background in Windows7. The feature is just there, only hidden, especially when your system is installed from a retail version DVD, rather than factory preloaded or imaged from the OEM Recovery Media .

Totally, 3 steps are necessary, and sufficient.

a, Add a dword value in your registry
Open registry editor, navigate to LOCAL_MACHINE/SOFTWARE/Microsoft/Windows/CurrentVersion/Authentication/LogonUI/Background/
Add a dword valued named “OEMBackground” (if not exist) and assign a value “1” . Save and quit.
How to access registry?.. Press WinKey+R (or Command+R on MacBook running Windows OS), type “regedit”, enter.

b, Create a folder
One needs a folder called “backgrounds” at the following path
X:/Windows/System32/oobe/info
If you don’t have the folder “info” under “oobe”, just create it as well.

c, Drag a JPEG
Now you may want to select your favorite JPEG file (must be smaller than 250KB in volume) and throw it into
X:/Windows/System32/oobe/info/backgrounds,
rename it as “backgrounddefault.jpg” . For best experience, one is encouraged to resize that JPEG (using PS or MS Office Picture Manager) to fit the native resolution of your screen (or the width/height ratio at least), while keep its volume still under that 250KB limit.

Voila! Now you are ready to go. It takes effect immediately and you may see the new logon screen from the first time you logout.

Most of all, it’s totally clean and reversible. To switch back to the default Windows 7 logon background:
–simply change that DWORD value back to 0,
–or just delete the DWORD registry entry,
–or just delete that JPEG file.