Hi Harald,
It depends from what kind of restriction do you need to apply:
1) If you wish restrict by MLA doc-category editing of media library items, you can use “Edit restrictions” add-on. Just input categories list ID into the user profile or user role.
2) There is the “Content view restriction” add-on, which allows to manage who can view post/page content at front-end, including a category level. But you need to take into account here, that this add-on hides the post content only – the description for media library item. So if image is attached to the post you have to restrict the view of the whole post itself or the part of post with the image inside using shortcode. URE does not restrict view of media library item (image, PDF file, etc.) via direct URL. It works with the post content only.
