Xianming Liu Hongxun Yao Rongrong Ji Pengfei Xu Xiaoshuai Sun What is a complete set of keywords for image description & annotation on the web. 613-616 2009 ACM Multimedia http://doi.acm.org/10.1145/1631272.1631369 conf/mm/2009 db/conf/mm/mm2009.html#LiuYJXS09