La metti in un div e centri il div
codice:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Documento senza titolo</title>
<style type="text/css">
#immagine {
position: absolute;
width: 200px;
height: 200px;
top: 50%;
left: 50%;
margin: -100px 0 0 -100px;
}
</style>
</head>
<body>
<div id="immagine">
[img]immagine.jpg[/img]
</div>
</body>
<div id="immagine">
</html>