parseListContent.php

<?php
$html = '<ul>
<li><a href=""><img src="http://..."></a></li>
<li><a href=""><img src="http://..."></a></li>
<li><img src="http://..."></li>
<li><a href=""><img src="http://..."></a></li>
</ul>';

$dom = new DomDocument();
$dom->loadHTML($html);
$xpath = new DOMXPath($dom);

foreach($xpath->query('//li') as $li)
{
  foreach($li->childNodes as $item)
    {
        var_dump($dom->saveHTML($item));
    }
}
?>