从JS开始：

$(\'#logo_upload\').click(function () {
            var file_data = $(\'#upload_image\').prop(\'files\')[0];
            var form_data = new FormData();
            form_data.append(\'upload_image\', file_data);
            form_data.append(\'action\', \'uploadImages\');
            form_data.append(\'security\', wp[\'security\']);
            form_data.append(\'nome_associazione\', $(\'.nome-associazione\').html());
            form_data.append(\'ID\', $(this).data(\'post\'));
            $.ajax({
                type: \'POST\',
                url: wp[\'ajaxUrl\'],
                processData: false,
                contentType: false,
                data: form_data,
                success: function (response) {
                    console.log(response);
                },
                error: function (error) {
                    if (error.status === 403) {
                        location.reload();
                    }
                },
            });
        });

PHP：

public static function uploadImages() {
        self::checkAjaxReferer();
        $params = self::parseParams($_POST[\'params\']);
        $associazione = str_replace(" ", "-", $params[\'nome_associazione\']);
        $postID  = $params[\'ID\'];

        if (isset($_FILES[\'upload_image\']))
        {
                $file_name = \'logo-\'.$associazione."-".$_FILES[\'upload_image\'][\'name\'];
                $file_size = $_FILES[\'upload_image\'][\'size\'];
                $file_tmp = $_FILES[\'upload_image\'][\'tmp_name\'];
                $file_type = $_FILES[\'upload_image\'][\'type\'];
                $uploadedfile = $file_name;
                $upload_name = $file_name;
                $uploads = wp_upload_dir();

                $filepath = $uploads[\'path\'] . "/" . $upload_name;
                if (!function_exists(\'wp_handle_upload\')) {
                    require_once(ABSPATH . \'wp-admin/includes/file.php\');
                }

                require_once(ABSPATH . \'wp-admin/includes/file.php\');
                require_once(ABSPATH . \'wp-admin/includes/image.php\');

                $upload_overrides = array(
                    \'test_form\' => false
                );

                $movefile = wp_handle_upload($uploadedfile, $upload_overrides);

                if ($movefile && !isset($movefile[\'error\'])) {
                    $file = $movefile[\'file\'];
                    $url = $movefile[\'url\'];
                    $type = $movefile[\'type\'];

                    // media_handle_upload( $file_handler, 0 );

                    $attachment = array(
                        \'post_mime_type\' => $type,
                        \'post_title\' => \'logo-\' . $associazione,
                        \'post_content\' => \'Image for \' . $upload_name,
                        \'post_status\' => \'inherit\',
                        \'post_parent\' => $postID
                        //\'post_parent\' => 0 //IF DONT WANT TO ATTACH POST ID
                    );
                    $attach_id = wp_insert_attachment($attachment, $file, $postID);
                    //$attach_id = wp_insert_attachment($attachment, $file, 0);//IF DONT WANT TO ATTACH POST ID

                    $attach_data = wp_generate_attachment_metadata($attach_id, $file);
                    wp_update_attachment_metadata($attach_id, $attach_data);

                    echo wp_insert_post($my_post);
                }
                else {
                         die($movefile[\'error\']);
                }

        }
    }