How I can show a Metabox with thumbnails of images attached to a post / page without adding a meta key to avoid this metabox as a custom field ?
I need to use the default attachment "meta key" provided by WordPress, or something similar, to showing in post edit screen all images attached as thumbnail, and after, use this images attached in a post/page template to use a query with pagination
To show all attached images of the being edited post, you need to write custom code to get them and put them in the custom_html field. This field doesn't have any input and don't save anything to the database. You can use it just to show the content you want.