#!/usr/bin/perl
#
#
use strict;
use warnings;

use Glib;
use Gtk2 -init;

my $builder = Gtk2::Builder->new();
$builder->add_from_file("image_gtk.glade");
$builder->connect_signals(undef);

Gtk2->main;

sub filechooserbutton1_file_set_cb {
    my $filename = shift @_;
    my $image = $builder->get_object('image1');
    $image->set_from_file($filename);# wrong
    $image->set_from_file($filename->get_filename); #right, this makes it work
}