The photo plugin queries photos from flickr and shows them on the map. With the API parameters currently supplied, the following restriction [1] applies to the result: 
"Geo queries require some sort of limiting agent in order to prevent the database from crying. This is basically like the check against "parameterless searches" for queries without a geo component. 
A tag, for instance, is considered a limiting agent as are user defined min_date_taken and min_date_upload parameters — If no limiting factor is passed we return only photos added in the last 12 hours (though we may extend the limit in the future)."

In practice this means that when zooming in to ~ city level or higher, most times no photos show up any more - even though flickr would provide many for the area.

The 12 hour check can be gamed by restricting the returned photos to all available licenses (append "&license=1,2,3,4,5,6,7" to the http call), but that's not a sane behavior in general.

Unless someone has a better idea, I'd suggest to check the size of the bounding box and lift the 12 hour restriction in the http call for higher zoom levels (small bounding box). This would mean that for higher zoom levels only new flickr photos show up and for city level and higher all photos of the given area.

[1] http://www.flickr.com/services/api/flickr.photos.search.html


Reproducible: Always