Apple has announced Shared Photo Streams, a method to share and comment on pictures in Photo Streams on iOS, Apple TV, OS X apps like Aperture, and on a web browser. After picking photos and friends to be shared, users can share pictures in album form, and friends will get a notification when they're uploaded. From there, users can "Like" or add comments to the pictures. It's another try at social features for Apple, and one that seems more organic than the now forgotten Ping. That may be partly because it's very, very similar to Facebook's own features. It should work across just about any platform you can think of, so long as it's Apple's.