I give a lot of presentations, and the background picture of my baby alpaca, while fascinating to me, probably does not have the same level of attraction to my clients. I know I can mouse around and change the desktop picture to some bland color, but I prefer to run a script and make the change because I can have the same script close Office Outlook and launch my presentation slides as well. I know how to use the Stop-Process cmdlet to stop Office Outlook, and it is a no-brainer to start my PowerPoint slide show. However, I am stumped at changing the background picture of my baby alpaca. I tried to use WMI, but the Win32_Desktop class does not seem to allow updates. Do you have any suggestions?

– JP

Hi JP,

I have a great suggestion—leave the alpaca desktop. I think they are great pets. I fell in love with them when I was working in Peru. I have a blanket made from baby alpaca fur that I use when I am reading beside the fireplace in the evening. Besides, alpacas are very polite animals and have wonderful dispositions. But because you have already decided to hide the alpaca during presentations, I guess I will show you how to use the registry to make the required changes. (Now if you had said you were getting rid of a picture of a cat, I would willingly help you. As it is, I am helping under protest.)

The Get-SetDesktopBackground.ps1 script will allow you to retrieve the desktop background picture via the registry. It will also allow you to set the desktop background picture as well. The Get-SetDesktopBackground.ps1 script is seen here.

Get-SetDesktopBackground.ps1

Function Get-WallPaper()
{
 $wp=Get-ItemProperty -path 'HKCU:\Control Panel\Desktop\' -name wallpaper
 if(!$wp.WallPaper)
   { "Wall paper is not set" }
 Else
  {"Wall paper is set to $($wp.WallPaper)" }
}
Function Set-WallPaper($Value)
{
 Set-ItemProperty -path 'HKCU:\Control Panel\Desktop\' -name wallpaper -value $value
 rundll32.exe user32.dll, UpdatePerUserSystemParameters
}
Get-WallPaper
Set-WallPaper -value ""
Get-WallPaper

In the Get-SetDesktopBackground.ps1 script, we begin with a function that retrieves the background information from the registry. The registry key is seen here:

To read the value from the registry, we can use the Get-ItemProperty cmdlet from Windows PowerShell. When using the Get-ItemProperty cmdlet, we need to give it the path to the registry key and the name of the registry key property to retrieve. The cool thing about Windows PowerShell is there is a thing that is called a registry provider. The registry provider exposes the registry as if it were a drive. You can type dir HKCU:\ if you wish, and you will obtain a directory listing of registry keys. It is way cool (not merely plain old cool)!

If we were to use the Get-ItemProperty cmdlet to retrieve the wallpaper settings directly, we would retrieve a custom Windows PowerShell object that contains a lot of information about the registry key, as well as the property value. This is seen here:

PS C:\> Get-ItemProperty -path 'HKCU:\Control Panel\Desktop\' -name wallpaper
PSPath       : Microsoft.PowerShell.Core\Registry::HKEY_CURRENT_USER\Control Panel\Desktop\
PSParentPath : Microsoft.PowerShell.Core\Registry::HKEY_CURRENT_USER\Control Panel
PSChildName  : Desktop
PSDrive      : HKCU
PSProvider   : Microsoft.PowerShell.Core\Registry
Wallpaper    : C:\Windows\zapotec.bmp

We are only interested in the value of the wallpaper setting. We store this custom object in the $wp variable, and then we check to see if there is a value for the wallpaper. If there is no entry in the registry key, there is no wallpaper set. This is seen here:

If there is a value for the registry key property, it is displayed. The complete Get-WallPaper function is seen here:

Function Get-WallPaper()
{
 $wp=Get-ItemProperty -path 'HKCU:\Control Panel\Desktop\' -name wallpaper
 if(!$wp.WallPaper)
   { "Wall paper is not set" }
 Else
  {"Wall paper is set to $($wp.WallPaper)" }
}

To set the wallpaper, we use Set-ItemProperty instead of Get-ItemProperty. We again specify the path to the registry key, the name of the registry key property, and the new value we wish to set. The new value is supplied when the Set-WallPaper function is called. To ensure the changes to the wallpaper take place immediately, we call the rundll32.exe program and we feed it the user32.dll. We call the UpdatePerUserSystemParameters method to cause the new registry entry to take effect. This works great for setting system wallpapers, and turning off wallpapers. Depending on the image file you are working with, your success in getting this method to work will vary. The complete Set-WallPaper function is seen here:

Function Set-WallPaper($Value)
{
 Set-ItemProperty -path 'HKCU:\Control Panel\Desktop\' -name wallpaper -value $value
 rundll32.exe user32.dll, UpdatePerUserSystemParameters
}

To change the wall paper to zapotec.bmp, you would pass the path to the zapotec.bmp file when calling the function:

Set-WallPaper -value "C:\Windows\zapotec.bmp"

If you want to turn off the wall paper altogether, as was expressed in the e-mail we got from JP, you would call the function and pass it a set of empty quotation marks as is seen here:

Set-WallPaper –value ""

JP, that is all there is to getting and setting desktop wallpaper via the registry. This also concludes our Desktop Week articles. Join us tomorrow for Quick-Hits Friday, where we will tackle an assortment of short questions using both VBScript and Windows PowerShell in our answers. Until then, grab your alpaca blanket and stay warm.

Ed Wilson and Craig Liebendorfer, Scripting Guys