Have a new forum section called ‘Postcards’ or ‘Wish you were here’ or ‘Hello from ??’ or some such.
The forum allows for :-
One photo post per member in any 24 hour period.
Only photos taken within the past 24 hours .. so photo must have a date & time
Only photos with a location
In the photo caption .. Only 10 words of text or a max number of characters perhaps.
The photo disappears 24 hours after posting but remain in a member’s gallery.
At the top of the forum or maybe outside the forum someplace .. A ‘dark’ map of the world that lights up countries pinpointed by the photos locations .. getting brighter & dimmer depending on the number of photos for a country.
Notification of posting would default to off but notifications could go to ‘friends’ if allowed by a friend.
How to keep out junk? Limit posts to members of a certain status. Keep it clean .. No nudity or disgusting photos, pause or inactivate membership for abuse.
Allow for comments on the photo or not?