yeah the url_id is the row id.
so you will have a php script that prints your image and link.
echo "<A href='loadurl.php?id=$url_id'><img src='Upload/$image' height=25 width=100 border=0></A> ";
then have your loadurl.php get the id $GET['id']
and then query the database SELECT url FROM imageurls WHERE id = '$GET['id']
then get your real URL from the query (say $url)
then header('Location: ' . $url);