How do image sharing websites such as imgur, photobucket and imgFap keep out illegal images?<p>Do they have a team of moderators keeping an eye on things or is there some type of algorithm they use to detect the images?
They don't. Recommended reading: DMCA safe harbor provision <a href="https://en.wikipedia.org/wiki/Digital_Millennium_Copyright_Act#Title_II:_Online_Copyright_Infringement_Liability_Limitation_Act" rel="nofollow">https://en.wikipedia.org/wiki/Digital_Millennium_Copyright_A...</a> and related. In other words, things get taken down by nastygrams from lawyers, not by algorithm.<p>Note that images may be "illegal" for approximately ten bazillion different reasons, and most of those reasons can't be determined algorithmically - from copyright infringement to pornography (famously defined as "I know it when I see it").
They usually have a "report photo" link.<p>I assume a human may review the reports and wields the ignore/delete/banhammer as appropriate.<p>If I were to build one, I'd ensure I kept a hash/perceptual hash (see phash and friends) of removed images so they'd get put in the queue/automatically rejected as appropriate.
Companies can have teams of content moderators or reviewers, whether employees or outsourced.<p>Good article is here: <a href="http://www.nytimes.com/2010/07/19/technology/19screen.html?_r=0" rel="nofollow">http://www.nytimes.com/2010/07/19/technology/19screen.html?_...</a>