In case of missing or broken file links the article page associated with will get the "Pages with broken file links" maintenance category. But this is not very helpful if the image is not visibly shown at the page. There are three cases known to me:

1. The image is part of a scroll gallery but not its first element.
2. The image is part of the description for the <maplink> tag. So the image is shown only on the map but not on the article page.
3. The image is part of a container with the display attribute none.

In both cases it is very time-consuming to search for these images. In the second case we are using the Lua call mw.title.new('Media:' .. image) to detect broken file links. But this call is very expensive. My proposal to have a less-expensive call (T179636) was declined.

Maybe the names of the broken file links can be given in the head in preview mode similar to the case of duplicated template parameters, in the Parser profiling data section, or at the Page information.