Типа вот этого?
require_once("config.php");
$doc=mysql_query("Select picture from product");
header("Cache-Control: public, must-revalidate");
header("Vary: Content-ID: ".md5(mysql_result($doc, 0, "picture")));
header("Content-type: ".mysql_result($doc, 0, "type"));
echo mysql_result($doc, 0, "picture");
mysql_close();
?>