EPiServer never indexes use of files that you have in your templates. Images used in templates should be separated from the content on the site to prevent editors from breaking the templates. The references shown in the file mangager are usages of files from content on the site, that is: references to the file from properties on content like pages and blocks.
In Episerver FileManagement some images have "no related pages" in filesummary, but there are pages, that use these pictures. Update, site restart, reindexing didn't help. Images are displayed by some control that gets image path from PropertyImageUrl (or some other, I tried PropertyString too) type property. Control is rendering like
But some images are just statically written tags with static src value like
No one of these approaches (use control or static tag) did not work on one new-added to episerver file system image - it still had "no related pages". But some other images in file manager has normally displaying related pages, rendering of these images on their related pages happens in the same way, as I described above. VPP providers are default, filesummary.config is default also. It just seems that some random images, that really are used, have no related pages in filesummary. This seems not to depend on the way images are displayed on pages. Maybe you have some information regarding the way Episerver creates "related pages" list in filesummary? What else can I try? Maybe it takes episerver a time to renew this information? Where it is stored?