Wordpress file upload media_handle_upload fatal error - php

Question

I wrote a PHP script to process files sent to it via POST.
On the frontend js script, I create a Formdata object, and append images to it...like:
formdata.append('image0', image0);
formdata.append('image1', image1);
etc
This is my PHP code, the code is in the wordpress root directory
<?php
header("Access-Control-Allow-Origin: *");
require_once('wp-admin/includes/image.php' );
require_once('wp-admin/includes/file.php' );
require_once('wp-admin/includes/media.php' );
$id_array = array();
$c = 0;
foreach ($_FILES as $file) {
$id_array[] = media_handle_upload('image' . $c, 0);
$c++;
}
echo implode(',', $id_array);
However when I run this code, I get the following error:
Fatal error: Call to undefined function __() in /home/website/public_html/wp-admin/includes/file.php on line 16
Am i missing to include additional files in the script? I used the documentation on wordpress and it said:
These files need to be included as dependencies when on the front end.
require_once( ABSPATH . 'wp-admin/includes/image.php' );
require_once( ABSPATH . 'wp-admin/includes/file.php' );
require_once( ABSPATH . 'wp-admin/includes/media.php' );
I would appreciate any help!

Answer 1

In order to use the native Wordpress functions, such as __() wp-config.php needs to be included additionally.
Adding wp-config.php solved the issue

Answer 2

I'm also facing same issue.
Adding this in functions.php will fix the error.
Some time it will show as "http error"
add_filter( 'wp_image_editors', 'raj_change_graphic_library' );
function raj_change_graphic_library($array) {
return array( 'WP_Image_Editor_GD', 'WP_Image_Editor_Imagick' );
}