Despite this image www.flickr.com/photos/cwaterjohn/3949980541
being set on privacy for friends and family only, someone has within the last 45 minutes added it as one of their favourites.
I wonder on what basis they were able to access my image without being either friend or family? I suspect like much else their privacy settings are all screwed up...

Flickr responded to my complaint:
Thank you for contacting Yahoo! Flickr.
I verified this is a valid issue on Flickr and I've escalated it to our product team to identify the cause. They'll review the issue and work toward a solution. I apologize for any inconvenience this has caused.
Thank you for bringing this to our attention. Our goal is to create a positive experience for all of our members, and you are helping us to do that.

So it appears there is a problem with their privacy settings. In my case it's no big deal, but for those who have images they imagine as set to be viewed only by themselves, they may be in for a very rude awakening!