[Reflection.Assembly]::LoadWithPartialName("System.Drawing")
function screenshot([Drawing.Rectangle]$bounds,$path) {
   $bmp = New-Object Drawing.Bitmap $bounds.width,$bounds.height
   $graphics = [Drawing.Graphics]::FromImage($bmp)

   $graphics.CopyFromScreen($bounds.Location,[Drawing.Point]::Empty,$bounds.size)

   $bmp.Save($path)

   $graphics.Dispose()
   $bmp.Dispose()
}

$bounds = [Drawing.Rectangle]::FromLTRB(0,1000,900)
screenshot $bounds "C:\screenshot.png"