Since ImageMagick is not available, I have to use GD, but I can't manage to resize a picture with it, it becomes black...
|$image_p = imagecreatetruecolor(640, 480);
list($width, $heigth) = getimagesize($_FILES['picture']['tmp_name']);
$image = imagecreatefromjpeg($_FILES['picture']['tmp_name']);
imagecopyresampled($image_p, $image, 0, 0, 0, 0, 640, 480, $width, $height);
imagejpeg($image_p, $uploadfile, 85);