上载的图像未保存到文件夹中

我有一个html上传表单，它由image-crop.php处理。我想在上传完成后将图像保存到img文件夹中。但它并没有将图像保存到img文件夹中。为什么图像没有保存到该文件夹，有什么建议吗？

Html形式：

<form action="image-crop-demo.php" method="post" enctype="multipart/form-data">
    Upload an image for processing<br>
    <input type="file" name="Image1"><br>
    <input type="submit" value="Upload">
</form>

Php代码：

define('DESIRED_IMAGE_WIDTH', 200);
define('DESIRED_IMAGE_HEIGHT', 200);
$source_path = $_FILES['Image1']['tmp_name'];
list($source_width, $source_height, $source_type) = getimagesize($source_path);
switch ($source_type) {
    case IMAGETYPE_GIF:
        $source_gdim = imagecreatefromgif($source_path);
        break;
    case IMAGETYPE_JPEG:
        $source_gdim = imagecreatefromjpeg($source_path);
        break;
    case IMAGETYPE_PNG:
        $source_gdim = imagecreatefrompng($source_path);
        break;
}
$source_aspect_ratio = $source_width / $source_height;
$desired_aspect_ratio = DESIRED_IMAGE_WIDTH / DESIRED_IMAGE_HEIGHT;
if ($source_aspect_ratio > $desired_aspect_ratio) {
    $temp_height = DESIRED_IMAGE_HEIGHT;
    $temp_width = ( int ) (DESIRED_IMAGE_HEIGHT * $source_aspect_ratio);
} else {
    $temp_width = DESIRED_IMAGE_WIDTH;
    $temp_height = ( int ) (DESIRED_IMAGE_WIDTH / $source_aspect_ratio);
}
$temp_gdim = imagecreatetruecolor($temp_width, $temp_height);
imagecopyresampled(
    $temp_gdim,
    $source_gdim,
    0, 0,
    0, 0,
    $temp_width, $temp_height,
    $source_width, $source_height
);
$x0 = ($temp_width - DESIRED_IMAGE_WIDTH) / 2;
$y0 = ($temp_height - DESIRED_IMAGE_HEIGHT) / 2;
$desired_gdim = imagecreatetruecolor(DESIRED_IMAGE_WIDTH, DESIRED_IMAGE_HEIGHT);
imagecopy(
    $desired_gdim,
    $temp_gdim,
    0, 0,
    $x0, $y0,
    DESIRED_IMAGE_WIDTH, DESIRED_IMAGE_HEIGHT
);
header('Content-type: image/jpeg');
imagejpeg($desired_gdim, "img/", $_FILES["file"]["name"]);

谢谢。