[Tracker] About nmm:Photo

[Matt Yung <matt yangzhipeng gmail com>]

Hi,
    I'm a new user of tracker and meet a problem. 
When I exec 
"SELECT nie:url(nie:isStoredAs(?photo)) nie:mimeType(?photo) ?photo WHERE{?photo a nmm:Photo}",
I got an empty result.
But when I exec 
"SELECT ?fileName WHERE { ?contact a nfo:FileDataObject; nfo:fileName ?fileName}", 
I got the files existed in the system including some jpg files. 

My question is what should I do to tracker can make nmm:Photo return the right file list.
And How could user set file types that can be chosen by nmm:Photo.


Best wishes,
Matt