追記

2022/2/15どうせ使うなら、今ならこれがよさそうですね。

https://stackoverflow.com/questions/2969321/how-can-i-do-a-screen-capture-in-Windows-powershell/44609221#44609221

参照がたりない

星空は撫子色 - PowerShell でスクリプト実行できなかった

のコードだとPowerShell Hostで実行すると参照ないとかいろいろ言われます。

Unable to find type [System.Windows.Forms.Screen]. Make sure that the assembly that contains this type is loaded.
At C:\Users\acquire\Desktop\Screenshot.ps1:2 char:1
+ $b = New-Object System.Drawing.Bitmap([System.Windows.Forms.Screen]::PrimaryScre ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : InvalidOperation: (System.Windows.Forms.Screen:TypeName) [], RuntimeException
    + FullyQualifiedErrorId : TypeNotFound

Unable to find type [System.Drawing.Graphics]. Make sure that the assembly that contains this type is loaded.
At C:\Users\acquire\Desktop\Screenshot.ps1:3 char:1
+ $g = [System.Drawing.Graphics]::FromImage($b)
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : InvalidOperation: (System.Drawing.Graphics:TypeName) [], RuntimeException
    + FullyQualifiedErrorId : TypeNotFound

New-Object : Cannot find type [System.Drawing.Point]: verify that the assembly containing this type is loaded.
At C:\Users\acquire\Desktop\Screenshot.ps1:4 char:20
+ $g.CopyFromScreen((New-Object System.Drawing.Point(0,0)),(New-Object System.Draw ...
+                    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : InvalidType: (:) [New-Object], PSArgumentException
    + FullyQualifiedErrorId : TypeNotFound,Microsoft.PowerShell.Commands.NewObjectCommand

You cannot call a method on a null-valued expression.
At C:\Users\acquire\Desktop\Screenshot.ps1:5 char:1
+ $g.Dispose()
+ ~~~~~~~~~~~~
    + CategoryInfo          : InvalidOperation: (:) [], RuntimeException
    + FullyQualifiedErrorId : InvokeMethodOnNull

You cannot call a method on a null-valued expression.
At C:\Users\acquire\Desktop\Screenshot.ps1:6 char:1
+ $b.Save((Join-Path .\Desktop $outImage))
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : InvalidOperation: (:) [], RuntimeException
    + FullyQualifiedErrorId : InvokeMethodOnNull

これは、 PowerShell ISEでは、デフォルトでSystem.Windows.Formsが参照されるけどPowerShellホストでは参照されないため。嫌ですよね、こういうの。で、参照をAdd-Typeで追加して、出力パスは環境変数でデスクトップを見るようにします。 *1

[string]$outImage ="screen.png"
Add-Type -AssemblyName System.Windows.Forms
$b = New-Object System.Drawing.Bitmap&#40[System.Windows.Forms.Screen]::PrimaryScreen.Bounds.Width,[System.Windows.Forms.Screen]::PrimaryScreen.Bounds.Height&#41
$g = [System.Drawing.Graphics]::FromImage&#40$b&#41
$g.CopyFromScreen&#40&#40New-Object System.Drawing.Point&#400,0&#41&#41,&#40New-Object System.Drawing.Point&#400,0&#41&#41,$b.Size&#41
$g.Dispose&#40&#41
$b.Save&#40&#40Join-Path $env:UserProfile\Desktop $outImage&#41&#41