With the current implementation, if two pictures have
exactly the same position, one hides the other. Even
with the highest zoom level.
When two pictures are at the same position or very
near one from another (like 10 meters, for example),
they should be shown as only one marker.
It should be like the group feature, but for all zoom
level, should not show the group icon and the popup
window (when you click the pin) should show all the
pictures at this location.
Note that you may have to add a scrollbar if there
are too many pictures.
To see an example, follow that URL and click on the
top most/left most pin: