function pic_wrapper($text) {
	$pattern = '/(<img.*alt=[\'"](.*)[\'"][^>]*>)/i';
	$replace = '<div class="pic"><div class="pic-img">\\1</div><div class="pic-capt">\\2</div></div>';
	return preg_replace($pattern, $replace, $text);
}
add_filter('the_content', 'pic_wrapper');