Not sure if everyone knows this already but it looks like when you tag a person in Facebook you are then automatically sharing that photo with anyone they are friends with. I didn't realize this until someone I didn't know "liked" one of my photos.
I know that by default I share all my content with friends only, not friends of friends. I'm not sure if this changed recently but check out the screenshot that shows the message that my photo is shared with my friends and anyone that is a friend of the people I've tagged.
I’ve updated Wordbooker and turned on advanced logging.