using namespace System.Drawing
Add-Type -AssemblyName System.Drawing # Specify System.Drawing.Common on PS Core

$filename = 'DSCI0001.jpg'
$filepath =  'C:\Users\Michael\Pictures\AllPictures\'
$filepathComplete = $filepath + $filename
$copyFilenameComplete = $filepath + 'copy' + $filename

Copy-Item -Path $filepathComplete -Destination $copyFilenameComplete

$BitMap = [Bitmap]::FromFile((Resolve-Path $filepathComplete).ProviderPath)

$rotWerte = 0
$anzahlPixel = 0
foreach($h in 1..$BitMap.Height){
  foreach($w in 1..$BitMap.Width) {
    $rotWerte = $rotWerte + $BitMap.GetPixel($w - 1,$h - 1).R
	$anzahlPixel = $anzahlPixel + 1
  }
}
$rotDurchschnittsWert = $rotWerte / $anzahlPixel
$newFileName = 'red' + $rotDurchschnittsWert + "__" + $filename

Rename-Item $copyFilenameComplete $newFileName