i used (basically taken from the docs)

use PDF::Reuse;
use Image::Info qw(image_info dim);
use strict;

my $file = 'c:/kopie.jpg';
my $info = image_info($file);
my ($width, $height) = dim($info);    # Get the dimensions

prFile('c:/myFile.pdf');


my $intName = prJpeg("$file", $width, $height);

my $str = "q\n";
$str   .= "$width 500 500 $height 100 100 cm\n";
$str   .= "/$intName Do\n";
$str   .= "Q\n";


prDoc('c:/anlage-h-rbskt.pdf');
prAdd($str);

prEnd();
[download]

but as i said, this will add the image to a new page. am i missing something?

it will also be ok if i could just add text to the background.