I think there is an interesting gray area here actually that I haven't seen discussed.

Randi posted the picture as "friends only" but due to Facebook's policies it turns out that people other than those friends could see the picture.

First question: If a friend posts something as "friends only" are you ethically bound not to publicly share it? I think most people would answer YES, under the assumption that if they wanted to make it public they would have posted it publicly.

But there are a couple of interesting wrinkles here :

1. Facebook's interface did not make it clear to Callie that this was a "friends only" post. Because it showed up in her feed she assumed it was public and meant for public consumption.

2. The presence of Mark Zuckerberg in the picture. Zuckerberg is essentially a celebrity and it seems there is a widespread assumption that ANY picture with a celebrity in it (whether Justin Bieber or President Obama) is fair game for sharing in a way that does not apply to non celebrities. I think if the picture did not include Mark Zuckerberg it is far less likely Callie or anyone else would have thought it was appropriate to share it.