$fullsize = $user_id . "_" . time() . "_" . $_FILES['shot']['name'];
$thumb = "thumb_" . $user_id . "_" . time() . "_" . $_FILES['shot']['name'];

move_uploaded_file( $_FILES['shot']['tmp_name'], $shot_directory . "/" . $fullsize );

list( $width, $height, $type, $attr ) = getimagesize( $shot_directory . "/" . $fullsize );

if ( $type == 1 )
    $src = imagecreatefromgif( $shot_directory . "/" . $fullsize );
else if ( $type == 2 )
    $src = imagecreatefromjpeg( $shot_directory . "/" . $fullsize );
else
    return "ERROR: This gallery only supports JPG and GIF file formats";

// creating a thumbnail ----------------------------------------------------------

$multiplier = 160 / $width;

$new_width = 160;
$new_height = round( $height * $multiplier );

if ( $new_height > 160 ) {
    $multiplier = 0;
    $new_height = 0;
    $new_width = 0;

    $multiplier = 160 / $height;

    $new_height = 160;
    $new_width = round( $width * $multiplier );
}

$dest = imagecreatetruecolor( $new_width, $new_height );

imageCopyResampled( $dest, $src, 0, 0, 0, 0, $new_width, $new_height, $width, $height );

imagejpeg( $dest, $shot_directory . "/" . $thumb );