Image file successfully uploaded using a Google App Engine application does not exist in bucket

I have the following code:

I create the application specific upload URL, using the method CloudStorageTools::createUploadUrl() as follows:

require_once 'google/appengine/api/cloud_storage  
/CloudStorageTools.php';
use google\appengine\api\cloud_storage\CloudStorageTools;

$options = [ 'gs_bucket_name' => 'myuserpics' ];
$upload_url =  
CloudStorageTools::createUploadUrl('/upload_handler.php', $options);

I Use the above URL as the action for the form I use to accept uploads, as follows:

<form action="<?php echo $upload_url?>"  
enctype="multipart/form-data"   method="post">
    Files to upload: <br>
    <input type="file" name="uploaded_files" size="40">
    <input type="submit" value="Send">
</form>

Below is the content of upload_handler.php:

<?php
    var_dump($_FILES);
?>

I start uploading to the above URL within 10 minutes of its creation and get the following output:

array(1) { 
    ["userfile"]=> array(5) { 
        ["name"]=> array(1) { 
            [0]=>   string(11) "fashion.jpg" 
        } 
        ["type"]=> array(1) { 
            [0]=> string(10) "image/jpeg" 
        } 
        ["tmp_name"]=> array(1) { 
            [0]=> string(200) "gs://myuserpics/***VERY LONG STRING***" 
        } 
        ["error"]=> array(1) { 
            [0]=> int(0) 
        } ["size"]=> array(1) { 
            [0]=> int(59527) 
        } 
    } 
} 

The permissions set for the bucket "myuserpics" are the default permissions.

When I look in the bucket, I do not see the uploaded image.

From the Google Developers Console, I am able to upload an image and then see it in the bucket. However, if an image is uploaded from the app, I cannot see it in the bucket. What am I doing wrong?