On-the-fly thumbnails PHP - php

Question

I came up with this:
<?php
$dir = $_GET['dir'];
header('Content-type: image/jpeg');
$create = imagecreatetruecolor(150, 150);
$img = imagecreatefromjpeg($dir);
imagecopyresampled($create, $img, 0, 0, 0, 0, 150, 150, 150, 150);
imagejpeg($create, null, 100);
?>
It works by accessing:
http://example.com/image.php?dir=thisistheimage.jpg
Which works fine... but the output is awful:
Can someone fix my code for the image to be 150 x 150 covering the black area...
Thanks.
SOLUTION:
<?php
$dir = $_GET['dir'];
header('Content-type: image/jpeg');
list($width, $height) = getimagesize($dir);
$create = imagecreatetruecolor(150, 150);
$img = imagecreatefromjpeg($dir);
$newwidth = 150;
$newheight = 150;
imagecopyresized($create, $img, 0, 0, 0, 0, $newwidth, $newheight, $width, $height);
imagejpeg($create, null, 100);
?>

Answer 1

Use imagecopyresized:
$newwidth = 150;
$newheight = 150;
imagecopyresized($create, $image, 0, 0, 0, 0, $newwidth, $newheight, $oldwidth, $oldheight);

Answer 2

The last 2 150 should be the original width and height of the full sized image.

Answer 3

As others suggested, last two parameters should be original size of the image.
If $dir is your filename, you can use getimagesize to obtain picture's original dimensions.
You can use imagecopyresized or imagecopyresampled. Difference is that imagecopyresized will copy and resize while imagecopyresampled will also resample your image which will yield better quality.
<?php
$dir = $_GET['dir'];
header('Content-type: image/jpeg');
$create = imagecreatetruecolor(150, 150);
$img = imagecreatefromjpeg($dir);
list($width, $height) = getimagesize($dir);
imagecopyresampled($create, $img, 0, 0, 0, 0, 150, 150, $width, $height);
imagejpeg($create, null, 100);
?>