PHP image resize not working

Question

I'm trying to create a thumbnail from a JPG image, but I can't get the resized image to output properly ("contains errors").

Here's my code, I can't figure out what's wrong:

<?php   
header('Content-Type: image/jpeg');

$photos = glob($_GET['a'] . '/*.*');
$img = imagecreatefromjpeg($photos[array_rand($photos)]);

list($width, $height) = getimagesize($img);
if($width > $height) {
    $newWidth = 250;
    $newHeight = 250*$height/$width;
}
else {
    $newHeight = 250;
    $newWidth = 250*$width/$height;
}

$tmp = imagecreatetruecolor($newWidth, $newHeight);
imagecopyresampled($tmp, $img, 0, 0, 0, 0, $newWidth, $newHeight, $width, $height);

// Output the image
imagejpeg($tmp);
?>

Answer 1

The function getimagesize() requires a filename, not an image resource. It emits a warning, that's why the image was not valid, because there is a string before the image binary.

$photos = glob($_GET['a'] . '/*.*');
$filename = $photos[array_rand($photos)] ;
$img = imagecreatefromjpeg($filename);
list($width, $height) = getimagesize($filename);

or use imagesx() and imagesy() to get image size using $img.

$photos = glob($_GET['a'] . '/*.*');
$img = imagecreatefromjpeg($photos[array_rand($photos)]);
$width = imagesx($img);
$height = imagesy($img);