* @return the thumbnail source URL if found, null otherwise
     */
    protected String getThumbnailSrc(final String url, final NamedNodeMap attributes) {
        final Node srcNode = attributes.getNamedItem("src");
        if (srcNode != null) {
            try {
                final URL thumbnailUrl = getURL(url, srcNode.getTextContent());
                if (thumbnailUrl != null) {