If you are a group administrator, you can invite your members to share and view photos from past events. To do this:

• Click on the event. (You can find a past event by clicking on "my calendar" and viewing your group's events).
• Click "photos."
• Click "View & share event photos" in the pop-up box.
• Click "invite attendees to share photos." 
• This will allow you to send your members a notification email to invite them to share event photos.