Is there a way of making iPhoto's Photo Stream one-way sharing?
Under iPhoto / Preferences / Photo Stream you can disable Automatic Upload. When turned off, you'll have to manually select which photos will be shared on the Photo Stream.



There are several ways of manually adding photos to the photo stream. After selecting the photos you want to share just:


Click the Share button in the toolbar, choose Photo Stream from the pop-up menu, and click My Photo Stream.
Click the Add To button in the toolbar, choose Photo Stream from the pop-up menu, and click My Photo Stream.
Choose Share / Photo Stream, and click My Photo Stream.