The shocking statistics reflect a growing demand for child abuse images online, the IWF says. Most of the pictures currently available are of females, the vast majority of whom are under 12 years old.
"Sadly, we have to report new trends regarding the young age of the child victims in the images we assess and the dreadful severity of abuse they are suffering and these facts, coupled with the longevity of some commercial websites, mean the victims' abuse can be perpetuated for many years as the images are repeatedly viewed," IWF chief executive Peter Robbins said.
More than four-fifths of the images available on the internet now originate from the US or Russia, while UK-based sites account for less than one per cent of the 3,077 sites the IWF says hosting the illegal images.
Catching the perpetrators can be difficult, today's report warns, because commercial child abuse websites store their images remotely and even, in some cases, in fragments.
"By distancing the parent site from the actual images and breaking up the image itself, those operating commercial child abuse websites are clearly trying to protect their content from removal and complicate the detection process," the report notes.
Commenting on the IWF's findings, home office minister Vernon Coaker said: "The IWF has made dramatic and continued progress in tackling the availability of illegal images of child abuse and has made a significant and ongoing contribution to the eradication of exploitation sites hosted in the UK, and the prevention of access to sites hosted abroad."
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