function disp($pid) {
        echo "<img src=pic-".$pid.".JPG>";
        echo "<br><br>";
        if (file_exists("pic-".($pid-1).".JPG")) {
        echo "<b><a href=photo.php?pid=".($pid-1).">Previous</a> &nbsp; </b>";
        }
        if (file_exists("pic-".($pid+1).".JPG")) {
        echo "<b><a href=photo.php?pid=".($pid+1).">Next</a></b>";
        }
}
if ($_GET['pid']) {
        disp($_GET['pid']);
} else {
        disp(1);
}