Why image cannot align to center?

Hello, all. I’m trying to modify the 404 page, I added a picture but it cannot align to center, only can align to right and left. Please help!~
—————————–
get_header(); ?>

<div id=”container”>

<div id=”content” role=”main”>

<div id=”post-0″ class=”post error404 not-found”>
<h1 class=”entry-title”><?php _e( ‘Page Not Found. Perhaps searching will help.’, ‘mantra’ ); ?></h1>
<div class=”entry-content”>

<!–insert image–>
<div><img src=”https://www.XXXXXXX.com/wp-content/uploads/2013/10/error-404.png&#8221; align=”center”></div>

</div><!– .entry-content –>
</div><!– #post-0 –>

</div><!– #content –>
<?php get_sidebar(); ?>
</div><!– #container –>
<script type=”text/javascript”>
// focus on search field after it has loaded
document.getElementById(‘s’) && document.getElementById(‘s’).focus();
</script>

<?php get_footer(); ?>