saintx arkadaşımız gerekli kodu vermiş ama alternatif olarak aşağıdaki gibi bir yöntemde uygulanabilir.

<?php
$string = '<?xml version="1.0" encoding="UTF-8"?>
<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9" xmlns:image="http://www.google.com/schemas/sitemap-image/1.1">
	<url>
		<loc>http://s.site_adi.com/veriler</loc>
		<priority>0.4</priority>
		<changefreq>daily</changefreq>
		<image:image>
			<image:loc>http://www.site_adi.com/yuklemeler/kucuk/s_veriler.jpg</image:loc>
			<image:caption>veriler</image:caption>
			<image:title>s veriler</image:title>
		</image:image>
		<image:image>
			<image:loc>http://www.site_adi.com/yuklemeler/o.../s_veriler.jpg</image:loc>
			<image:caption>veriler</image:caption>
			<image:title>s veriler</image:title>
		</image:image>
	</url>
</urlset>';

$string=preg_replace('/image:(.*?)>/i','$1>',$string);

$data = simplexml_load_string($string);
print_r($data);
?>