As Super Admin, I just posted a photo on an event page story board.
For non-logged in users, it shows up and is accessible on the main site story board.. but if you try and view it directly with its unique URL it says privacy restricted (which explains why only logged in users can see it on the event page too).
I'm not sure if this is a bug or a privacy setting - but I can't see any privacy settings which would appear to be the cause of this.
I'm providing all the links in the additional info section of this post.
Thanks for any help!