Alison Bosson Gavin C. Cawley Yi Chan Richard Harvey Non-retrieval: Blocking Pornographic Images. 50-60 2002 conf/civr/2002 CIVR http://link.springer.de/link/service/series/0558/bibs/2383/23830050.htm db/conf/civr/civr2002.html#BossonCCH02