Guest Passes let you share your photos that aren't public.
Anyone can see your public photos anytime, whether they're a Flickr member or not. But! If you want to share photos marked as friends, family or private, use a Guest Pass.
If you're sharing photos from a set, you can create a Guest Pass that includes any of your photos marked as friends, family, or private. If you're sharing your entire photostream, you can create a Guest Pass that includes photos marked as friends or family (but not your private photos).
Show machine tags (