watermarks with Imager What am I doing wrong?

[Scott]

#! /usr/local/bin/perl5

use strict;
use warnings;
use CGI;
use Imager;
my $query=new CGI;
my $img = Imager->new(file=>'filename.jpg') or die Imager->errstr();;
$img->filter(type=>'watermark', wmark => Imager->new('watermark.jpg'),
tx=>'10', ty=>'50', pixdiff=>'50')
or die $img->errstr;
print $query->header;
print "$img";
print $query->end_html;