I've noticed that if I add the same photo to a photo stream more than once, iPhoto is apparently not smart enough to recognize that it's a duplicate, and instead goes ahead and adds the photo a second (or third, etc.) time to the stream.
I would like to regularly drop certain photos into a photostream to share with a friend. But to do so, I need to know which photos I've not already shared in the past. It seems that the Smart Album logic cannot tell the membership status of photo streams, only local albums.
Is there a way to create a smart Album (or other method) that will show:
All photos in Album A and NOT in Photo Stream B?