Try this:
add in details.php below this line:
ShowImage($img_result, URL_IMAGE_ID."=".$image_id."&", 0);
this:
$site_template->register_vars(array("meta_description" => $img_result['image_description'],
"meta_keywords" => $img_result['image_keywords']
));
Then, add in template header.html:
<meta name="dc.description" content="{meta_description}">
<meta name="dc.keywords" content="{meta_keywords}">
Jan