<?php
/*
Copyright (c) 1999 Marcel Lemmen
       E-mail: lemmen@support.nl
       All  rights  reserved.
*/

$files=array( 'track01.mp3', 'escreen.exe');
$filenames=array( 'Thank ABBA for the music.mp3', 'Escreen.exe');
$additional_info=array( 'Various artists - Thanx ABBA for the music : 4978602 by
tes', 'Shareware program to make a screenshot: 529920 bytes');
$url= "/home/lemmen/public_html/data/";
/* When the files are on another server, use the
   whole address (http://www.server.com/dir/) in stead of /home/lemmen... */
       
$referer=ereg_replace( "\?.", "",$HTTP_REFERER); 
$thisfile= "http://$HTTP_HOST$PHP_SELF";
       
if ($referer!=$thisfile){
        echo "<center><big>Homepage: <a href=\"http://home.support.nl/~lemmen\">
http://home.support.nl/~lemmen</big><br><hr><br><br></center>";
        for ($i=0;$i<count($files);$i++)
        echo  "<P><A HREF=\"$PHP_SELF?$i\">",$filenames[$i], "</A> $additional_i
nfo[$i]\n";
}
else {
        $i=$QUERY_STRING;
        $total=$url . $files[$i];
        Header ( "Content-Type: application/octet-stream");
        Header ( "Content-Length: ".filesize($total));
        Header( "Content-Disposition: attachment; filename=$filenames[$i]");
        readfile($total);
}
?>

<img src="/display.php?id=34" border="0">With an ever changing ID of course. That's the part referencing my images in the database. The following is the code from the script which I use to retrieve the image from the database: 
<?

$connection=@mysql_connect(...);

@mysql_select_db(...);

$query="SELECT mime, file FROM images WHERE id=".$_GET["id"];

$rawdb=@mysql_query ($query,$connection);

if($rawdb AND @mysql_num_rows($rawdb)>0){

  $array=@ mysql_fetch_array($result);

  if (!empty($array["fileContents"])){

    // Output the MIME header

    header("Content-Type: ".$array["mime"]}");

    // Output the image

    echo $array["file"];

  }else{

    // something else...

  }

  @mysql_free_result($rawdb);

}else{

  // something else...

}

@mysql_close($connection);

?>Since I already have a session for each user that comes to my website, I just added the following: 
<img src="/display.php?id=34&sid=3839839039039393829" border="0">And implement a small session checkup in the script itself: 
<?

session_start();

if($_SESSION["is_known"]){

  // do database calls

}else{

  header("Location:http://mydomain.tld/dontstealmyimages.html");

}

?>