Attempting to set up photo sharing but trying to understand symbols

I am trying to set up photo sharing and have both the double people profile which shows I am sharing but their is another symbol at the bottom of some pictures that is a squeezed rectangle, showing higher heights on the long ends of the rectangle. What does this mean as I am having trouble sharing these pictures. Also, once someone has unsubscribed to an album in photo sharing, can you send a new invite and have them resubscribe?