protected static function strip_images($html) {
        // Load HTML and suppress any parsing errors (DOMDocument->loadHTML() does not current support HTML5 tags).
        $dom = new DOMDocument();
        libxml_use_internal_errors(true);
        $dom->loadHTML('<?xml version="1.0" encoding="UTF-8" ?>' . $html);
        libxml_clear_errors();

        // Find all img tags.
        if ($imgnodes = $dom->getElementsByTagName('img')) {
            // Replace img nodes with the img alt text without overriding DOM elements.
            for ($i = ($imgnodes->length - 1); $i >= 0; $i--) {
                $imgnode = $imgnodes->item($i);
                $alt = ($imgnode->hasAttribute('alt')) ? ' [ ' . $imgnode->getAttribute('alt') . ' ] ' : ' ';
                $textnode = $dom->createTextNode($alt);

                $imgnode->parentNode->replaceChild($textnode, $imgnode);
            }
        }
        $count = 1;
        return str_replace("<?xml version=\"1.0\" encoding=\"UTF-8\" ?>", "", $dom->saveHTML(), $count);
    }