I haven' t found anything perfect. There are always files that get through.
Here are my recommendations:
1. You can enable " Rate images by URL (blocked images will be replaced with blanks)" in Protection Profile. Sometimes this overblocks images, but will give you better protection from accidental porn.
2. I' ve found Bing image search to be much better than Google in terms of porn filtering. Bing put all their porn on the domain explicit.bing.net -- if you block that URL in the FTG, then you' ll get much less porn during regular image searches (assuming you' re using Bing). In the 4.1.x, you can even enforce safe image searches for users (although this doesn' t work for mobile users because of a bug/quirk/feature in the FTG filtering.)
3. If you need better coverage than that, then you' d need to move to a specialized server appliance/software that can detect fleshtones. We looked at something like this -- it' s supposed to be very good, but my guess you don' t want to spend add' l $$ here.
Bill
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Fortigate 600C 5.0.12, 111C 5.0.2
Logstash 1.4.1