More than 68,000 URLs hosting images and videos of children being sexually abused were taken offline 2015, the Internet Watch Foundation (IWF) has said.
The majority of the websites hosting either explicit photographs or videos of children being abused were discovered by the charity.
Of the abusive content removed, 69 per cent of it contained children who appeared to be ten-years-old or younger. A further breakdown estimated that three per cent of the materials included children younger than two. In 85 per cent of all images and videos the victims were girls.
"We're really seeing the abuse of image hosting services increasing year-on-year," Fred Langford the IWF's deputy CEO told WIRED. "They're posting images on image hosting sites – there are thousands of them out there – and they link to it."
The 68,092 URLs hosting the child sexual abuse content were traced back to 48 countries, the IWF said in its annual report. Of the top level domains hosting the webpages .com .net .ru .org and .se, when combined, accounted for 91 per cent of all webpages identified containing the images and videos.
The charity said it took action on 135 webpages hosting images and video in the UK and issued 34 takedown notices for them to be removed from the internet. "We might send one notice for several webpages and content may have already been removed by the time we get authorisation from the police," the IWF's report explained in its report. The charity also issued takedown notices against 18 companies who had their services "abused to host child sexual abuse images or videos".
In its 20 year history 660,000 reports have been made to the IWF. In 2015 the IWF received 112,875 reports of potentially illegal content; of these 49,334 reports came from the public and 63,641 reports were created by the IWF actively searching the internet for abuse images. Nearly half of all sites taken offline by the IWF for hosting illegal content were discovered by the charity, not the public.
A decline in public reports of child sexual abuse is linked to improved technology and powers for the IWF, according to Langford. Since April 2014 the charity has been allowed to run its own searches for child sexual abuse online, before this it could only act upon reports it had received from the public.
"We know we're disrupting the activity of these people as we get some quite negative feedback from peadophiles and we've equally seen the displacement and reduction of public reporting," Langford said.
The IWF is currently beta testing a targeted crawler that allows its searches to be semi-automated. The system, which creates a unique code or 'hash' of each image, can be used to find duplicates of that image. A similar system is being developed by Google to automatically detect videos of child sexual abuse.
The IWF, when trialling the hash system in 2015, gave the database to Facebook, Google, Microsoft, Twitter and Yahoo. As a result, from June to October 2015, the IWF added more than 19,000 of the most severe child sexual abuse images to its hash list.
"We're able to feed those hashes into a crawler, which will then go out and target particular areas where we know there is high activity," Langford said.
"It brings back those that they think are a match and it means that our analysts don't have to wade through lots of non-illegal content". As well as the hashes IWF members, which include internet companies and governments, are given a keyword list that may help them locate illegal content. In December 2015 there were 440 words on the list.
Despite progress, Langford doesn't believe an image and video scanning system will ever be fully automated. This, he explained, is because humans still need to be involved in the process to verify that the images are illegal and not false-positives.
Updated 21/04/16, 11:40: This article originally referred to child sexual abuse as 'child pornography'. This was an oversight and has now been amended.