Coming back to the simplicity of the picture example, I would have concerns about unforeseen uses of data that can potentially occur. The general rule is that once you've shared information on the Internet, it's difficult to guarantee that you'll have any right of retrieving that information; it could very well be out there for good. For example, if a user shares information through Facebook and Facebook has a third party application that's engineered and the user subsequently enters into an agreement to allow that app to use the data that the user has provided, what guarantee does the user have that the third party application developer won't necessarily go rogue?
There's a different transit of information. There's a transit from the user of that picture to Facebook, a use by the third party application developer of that photo. What does the third party application developer ultimately do with that photo? What uses could that have that are outside of Facebook's ability to recall and outside of the user's ability to retrieve? That would be a concern that I would have.