I believe it used to work this way but was switched off due to abuse - apparently people were creating fake accounts to bump up their own ratings. Now the pictures are chosen by people from the website's editorial team. Typically they will provide a justification for the pick, which you can see in the comments attached to the photo in the user's gallery.
The info you have seen is probably out of date.
TBPITW 29-30 Mar 2008 and 9-10 Aug 2008
DCM Gallery