Windowsでコマンドラインからウィンドウ部分だけを画面キャプチャーする

$src = '
using System;
using System.Runtime.InteropServices;
public static class WindowRect { // Ver.1.0
    [DllImport(@"User32.dll")] public extern static IntPtr GetForegroundWindow();
    [DllImport(@"Dwmapi.dll")] public extern static int DwmGetWindowAttribute(IntPtr h,uint a,ref RECT rc,int asize);
    [StructLayout(LayoutKind.Sequential)] public struct RECT {
        public int Left;
        public int Top;
        public int Right;
        public int Bottom;
    }
    public static RECT GetWRect(IntPtr hWnd)    {
        RECT rcWindow = new RECT();
        DwmGetWindowAttribute(hWnd, 9, ref rcWindow, Marshal.SizeOf(rcWindow) );
        return rcWindow;
    }
}
'
Add-Type -AssemblyName System.Drawing,System.Windows.Forms
try { Add-Type $src } catch {}
function global:Get-CaptureRect($myleft,$mytop,$myright,$mybottom){
    $Bmp=New-Object System.Drawing.Bitmap ($myright-$myleft),($mybottom-$mytop)
    ([System.Drawing.Graphics]::FromImage($Bmp)).CopyFromscreen($myleft,$mytop,0,0,$Bmp.size)
    return $Bmp
}
function global:Get-WindowCaptureByHandle($hWnd) {
    $Rect=[WindowRect]::GetWRect($hWnd)
    return (Get-CaptureRect $Rect.Top $Rect.Right $Rect.Bottom)
}
function global:Get-MonitorList(){
    $screens = [Windows.Forms.Screen]::AllScreens
    $screens | Sort-Object -Property DeviceName | ForEach-Object { Write-Output "$($_.DeviceName.substring(4)) $($_.Bounds.Left) $($_.Bounds.Top) $($_.Bounds.Right) $($_.Bounds.Bottom)"}
    Write-Output "Desktop : $([System.Linq.Enumerable]::Min([int[]]$screens.Bounds.Left)) $([System.Linq.Enumerable]::Min([int[]]$screens.Bounds.Top)) $([System.Linq.Enumerable]::Max([int[]]$screens.Bounds.Right)) $([System.Linq.Enumerable]::Max([int[]]$screens.Bounds.Bottom))"
}
function global:Save-CurrentWindowCapture() {
    $CaptureBmp=Get-WindowCaptureByHandle([WindowRect]::GetForegroundWindow())
    $Fname="C:\temp\P$(get-date -Format 'yyyyMMdd-hhmmss').png"
    $CaptureBmp.save($Fname)
    $CaptureBmp.dispose()
    return $Fname
}
#Start-Process (Save-CurrentWindowCapture)