The overblocking of Wikipedia because of one image on the IWF database, serves as a timely warning against more widespread filtering.

Filters put in place by UK ISPs to comply with a blacklist of child pornography websites have resulted in widespread blocking of the Wikipedia. In some cases, UK users cannot edit Wikipedia pages, in others it seems they cannot view it at all. The intended target of the block is a single image of an album cover from a German rock band called the Scorpions, which is hosted on some Wikipedia pages.  The over-blocking of Wikipedia  affects O2,  Virgin Media, Sky/Easynet, Plusnet, Demon, and TalkTalk.

When I checked it – I am on Demon Internet – I get a notice telling me

“Wikipedia has been added to an Internet Watch Foundation’s UK website blacklist, and your Internet service provider has decided to block part of your access. Unfortunately, the method they are using makes it impossible for us to differentiate between legitimate users and those abusing the site. As a result, we have been forced to block several IP addresses from editing Wikipedia.”

On my best understanding, the IWF would be legally correct to classify this image as illegal in the UK under the Sexual Offences Act 2003, because it displays an under-age girl in a sexually-explicit position. Given that situation, downloading this image – that is, opening a web page which displays the image – is illegal, as is holding it in your cache after you have closed the page.  

However, I have two comments. In the first instance, common sense should prevail. The IWF compiles its blacklist manually, and it seems that the image is an isolated one. If the image does not link to sites with further similar material, nor is it hosted on such a site, then surely the Notice and Take-down procedure should apply. Certainly, Notice and Take Down would be a better way of dealing with the matter, which would not disrupt other legitimate uses of Wikimedia.  

Even though technically, the IWF can't issue a Take-down Notice to a site outside the UK, again, common sense dictates that Wikipedia can be contacted, unlike the majority of the websites that the IWF is there to address. Wikipedia does have a legal counsel who could be contacted for this purpose. From reading the Administrator’s Noticeboard, it appears that no request was made, although it also appears that the Wikipedia editors have considered whether to take the image down anyway, but have decided not to for the moment, because that would be a form of censorship.

 I would note here that the role of the IWF is to deal with websites which share or trade in child pornography, and as such is  limited to content which passes certain legal tests; it is not a general arbiter of standards, taste and decency nor is it's role to censor.  It is also argued on the Wikipedia Administrator's Noticeboard that the image is not illegal in other countries, including the US, and that the IWF filters are blocking (and therefore censoring)  text on the Wikipedia webpages,  as Wikpedia's representative, David Gerard, pointed out on the BBC's Today Programme.  

Secondly, the blocking of this image serves as a timely warning to us all concerning the wider introduction of filtering, which some parts of the UK government are considering. The IWF database contains only 800-1200 urls. It is a small and limited list, and is managed under some clear criteria. This case of over-blocking is an unusual instance. If filtering is introduced more widely, and for other purposes, over- blocking will happen more often (over-blocking means that web sites and pages are unintentionally blocked along with the target page or site). 

For example, filtering to support copyright - under consideration by the BERR consultation on peer-to-peer filesharing - will involve databases of millions of urls. If ISPs are able to make an overblocking error like this when they only have to block 1200 URLs, how many errors will they make when asked to filter against millions? It is not difficult mathematics to scale up the error rate, and we can estimate thousands of sites being incorrectly blocked.