add_action( 'wp_ajax_handle_dropped_media', 'handle_dropped_media' );

// if you want to allow your visitors of your website to upload files, be cautious.
add_action( 'wp_ajax_nopriv_handle_dropped_media', 'handle_dropped_media' );



function handle_dropped_media() {
    status_header(200);

    $upload_dir = wp_upload_dir();
    $upload_path = $upload_dir['path'] . DIRECTORY_SEPARATOR;
    $num_files = count($_FILES['file']['tmp_name']);

    $newupload = 0;

    if ( !empty($_FILES) ) {
        $files = $_FILES;
        foreach($files as $file) {
            $newfile = array (
                    'name' => $file['name'],
                    'type' => $file['type'],
                    'tmp_name' => $file['tmp_name'],
                    'error' => $file['error'],
                    'size' => $file['size']
            );

            $_FILES = array('upload'=>$newfile);
            foreach($_FILES as $file => $array) {
                $newupload = media_handle_upload( $file, 0 );
            }
        }
    }

    echo $newupload;    
    die();
}