Radu Andrei Negoescu Brett Adams Dinh Q. Phung Svetha Venkatesh Daniel Gatica-Perez Flickr hypergroups. 813-816 2009 ACM Multimedia http://doi.acm.org/10.1145/1631272.1631421 conf/mm/2009 db/conf/mm/mm2009.html#NegoescuAPVG09