Change Wallpaper with a batch file

I would like to change the wallpaper on a machine by running a batch file. Here is what I have so far

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I have a script that is copying over wallpaper.bmp to c:\wallpaper.bmp

I have the following reg key changing:

[HKEY_CURRENT_USER\Control Panel\Desktop]
"Wallpaper"="C:\\wallpaper.bmp"

             

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But the wallpaper doesnt seem to be changing. I have verified the file is there, and the regkey has changed. I have also tried to log off and log back on, but the registry reverts back to the way it was.

I found a post that suggested running the following command to refresh the desktop (but that hasnt worked either)

%SystemRoot%\System32\RUNDLL32.EXE user32.dll, UpdatePerUserSystemParameters

                                

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