Adding Boolean or Tag to Image File Field
The module File Entity has it's own field widget "Editable file".

You have to change the image field to use this widget in manage form display of the content type.

Then add a new image in the node creation page and a button will appear to edit the custom fields inline.

The widget has no preview image. So you have to choose, if you want inline fields or preview images.

The File Entity module is a basic solution with a very simple user interface.

A complete media solution for D8 will be provided by the Drupal Media Initiative, here are the latest news:

http://janezurevc.name/releases-of-various-drupal-8-media-modules