So when I put screenshots in the weekly changelog post I need to manually mark each of them as publicly viewable in /file/, otherwise nobody can see them.
Revisions and Commits
If you're sure other users can't see them, update to HEAD.
If you believe other users can't see them because the file page says that the visibility policy isn't what you expect (in the page subheader), check the "attached" tab. Users who can see "attached" objects can also see the file. You can click the file policy in the subheader to learn policy rules, including this rule.