Blenderartists actually has a policy on this: FAQ (Work in Progress)
However, in the context of the Weekend Challenge this causes a few problems. If I’m not mistaken, tags can still only be added to entire topics/threads - and not to single images or posts. So, if there is an entry within the scope of the above rule, I’ll have to tag both the entry and voting thread “not save for work”, which will blur all images of all participants.
This is a little inconvenient, but for now, this seems to be the only thing we can do.