Several people have asked me for a way to view the most photographed monuments.
This tool is now implemented http://toolserver.org/~platonides/wlm/monuments.php
The most photographed monument from all countries* is Colombian 06-050, with more than 2000 photos. Although that identifier spans the old sector of the city of Tunja, so it's not really fair to compare it with 'conventional monuments' with are a statue or a building.
* Disclaimer: If your country doesn't use identifiers or removes the identifiers from the description page, it is obviosuly not properly represented there.