What about having a dynamic block included in the page using a plugin-list ? (include plugin)
You have your wiki page with the father permission (from category "visible to anonymous) and the image in a bloc with a filter to match the same category.
Depending of the use case, I was also thinking of the group plugin. You can create a "special" group that act like an on and off (but it will be more global).
... May be you can have it the other way around.
Have a single category per page + content together, IE: mypage(wiki page), mypageimage(file) with the categorised under "mypage" category and then you set THIS category permission on/off and it will be applied on all elements (wiki page and file)
Again it depends of your use case... and number of pages. 😉