The number of individual images showing children being raped and sexually tortured has quadrupled since 2003, according to the latest report from the Internet Watch Foundation (IWF).

The organisation said the latest figures and trends outlined in its 2006 Annual Report clearly show the need for an international body to be set up to tackle this crime.

The IWF, which monitors websites containing images of child abuse and informs relevant authorities in attempts to take them down, is deeply concerned by the apparent increase in demand for more severe images of child abuse.

Last year it found nearly six in ten commercial child abuse websites were selling images of children being raped; 29 per cent of all potentially illegal child abuse web addresses known to the IWF contain what it terms level four and five images (the worst).

The IWF also reveals that 80 per cent of the children in abusive images are female with nine in ten of these children appearing to be under 12 years old.

Photo sharing websites have also come under scrutiny. In 2004, no images posted on photo album sites were added to the IWF's database. But the organisation said they are increasingly being used by paedophiles to share child abuse images and now account for 10.5 per cent of web addresses confirmed to have child abuse content.

Peter Robbins QPM, CEO of IWF, said: "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."

Although the IWF reported that calls processed by its child abuse hotline had risen 34 per cent over the last year, it said the latest trends illustrate the enormous challenge faced in removing commercial child abuse websites from the web.

Some of the most prolific sites, many which have avoided closure for years, do so by hopping servers across different legal jurisdictions, helping to avoid detection and protect content; one site has been reported 224 times to the IWF since 2002 but remains in business by doing this.

Another method these sites use to avoid detection is fragmenting images, which the IWF said muddied the water. Not only does this help these sites protect their content and complicate the detection process, it can also make it difficult to prove if the law has been broken.

"Is an image just showing a child's arms or just a torso breaking the law?" explained Sarah Robertson of the IWF.

Although hosting child abuse content in the UK has been virtually eradicated, making this country "one of the most hostile online spaces in the world for those who want to use technology to exploit children", according to Jim Gamble, chief executive of the UK's Child Exploitation and Online Protection Centre, nine out of ten of commercial child abuse sites continue to be hosted in the US and Russia.

This and the current trends, according to Sarah Robertson, clearly show that despite ongoing international collaboration, a global body needs to be established to tackle the crime.

John Carr, internet safety consultant for children's charity, NCH said he echoed the IWF's calls.

"In June last year I published  the report, Out of Sight, Out of Mind and  I pinpointed the weaknesses in [these] international institutions. While we don't necessarily need a new organisation but we do need a new initiative that will bring together on a global basis all the relevant organisations," he said.

He said the UK showed how well collaboration could work.

"In 1997, 19 per cent of websites containing images of child abuse were hosted in the UK; now that figure is around 0.2 per cent. This has not happened by accident but thanks to the efforts relevant UK authorities and organisations have put in. We need to replicate this on a global basis," he said.

But he warned in order to stamp out child abuse online more funding was needed.

"The current bodies are under-funded and overstretched," he said.