Det kan du ikke. Du skal oprette et andet php-script for at returnere billeddataene, f.eks. getImage.php. Skift catalog.php til:
<body>
<img src="getImage.php?id=1" width="175" height="200" />
</body>
Så er getImage.php
<?php
$id = $_GET['id'];
// do some validation here to ensure id is safe
$link = mysql_connect("localhost", "root", "");
mysql_select_db("dvddb");
$sql = "SELECT dvdimage FROM dvd WHERE id=$id";
$result = mysql_query("$sql");
$row = mysql_fetch_assoc($result);
mysql_close($link);
header("Content-type: image/jpeg");
echo $row['dvdimage'];
?>