codice:
function insertImage(&$pos, &$images){
	$img = '<a class="nounderline" href="'.$images[$pos]['path_high'].'" rel="lightbox" title="'.$images[$pos]['note'].'"/>'.
			'<img class="foto_testo_contenuto" align="<align>"  src="'.$images[$pos]['path_low'].'" alt="'.$images[$pos]['note'].'"/>'.
		'</a>';
	return str_replace('<align>', $pos++ % 2 ? 'left' : 'right', $img);
}

$pos = 0;

$images = array();

while($ro_img = mysql_fetch_assoc($r_img))
	$images[] = $ro_img;

$output = preg_replace(
	'/<image>/e', 
	'insertImage($pos, $images)', 
	wordwrap($output, 300, "<image>")
);