$mw = new MainWindow (-title => "My Perl/Tk app");
my $newlogo = $mw->setIcon(-file => $imagedir."logo.ico");

##</code><code>##

convert logo.png logo.xpm

##</code><code>##

$mw = new MainWindow (-title => "My Perl/Tk app");
my $newlogo = $mw->Photo(-file => $imagedir."logo.xpm", -format => 'xpm');
$mw->Icon(-image => $newlogo);