my $driver = Selenium::Remote::Driver->new;
$driver->set_window_size(320, 480);
$driver->get('http://www.google.com/404');
 
my $white = Selenium::Screenshot->new(png => $driver->screenshot);
 
# Alter the page by turning the background blue
$driver->execute_script('document.getElementsByTagName("body")[0].style.backgroundColor = "blue"');
 
# Take another screenshot
my $blue = Selenium::Screenshot->new(png => $driver->screenshot);
 
unless ($white->compare($blue)) {
    my $diff_file = $white->difference($blue);
    print 'The images differ; see ' . $diff_file . ' for details';
}