Sample PowerShell script that shows you how to create a .BMP file of the display of a Hyper-V virtual machine.

SaveVMBitmap.ps1

function Get-VMScreenBMP {
[cmdletbinding()]
Param(
[string]$VMName,
[string]$Computername = $env:computername,
[string]$Path,
[switch]$Passthru
)

    $VMMS = Get-WmiObject -Namespace root\virtualization\v2 -Class Msvm_VirtualSystemManagementService -ComputerName $Computername
    $VMCS = Get-WmiObject -Namespace root\virtualization\v2 -Class Msvm_ComputerSystem -Filter "ElementName='$($VMName)'" -ComputerName $Computername

    # Get the resolution of the screen at the moment
    $video = $VMCS.GetRelated("Msvm_VideoHead")
    $xResolution = $video.CurrentHorizontalResolution
    $yResolution = $video.CurrentVerticalResolution

    # Get screenshot
    $image = $VMMS.GetVirtualSystemThumbnailImage($VMCS, $xResolution, $yResolution).ImageData

    # Transform into bitmap
    $BitMap = New-Object System.Drawing.Bitmap -Args $xResolution,$yResolution,Format16bppRgb565
    $Rect = New-Object System.Drawing.Rectangle 0,0,$xResolution,$yResolution
    $BmpData = $BitMap.LockBits($Rect,"ReadWrite","Format16bppRgb565")
    [System.Runtime.InteropServices.Marshal]::Copy($Image, 0, $BmpData.Scan0, $BmpData.Stride*$BmpData.Height)
    $BitMap.UnlockBits($BmpData)

    $bitmap.Save($path)

    If ($Passthru) {
        Get-Item $path
    }
    
}

BTW - the reason why I am not using the code this way is because this line:

$video = $VMCS.GetRelated("Msvm_VideoHead")

Is quite expensive (it takes about 300ms). So if you are just getting a bitmap once - this is fine. However, if you are calling this repeatedly - you just want to get this information and cache it.