Fifty percent of Internet images showing sexual abuse of children are traced to the United States, and many of the images are available for years after a complaint is filed, according to a report released by the Internet Watch Foundation.

The IWF released a report Thursday on trends in online child abuse. It found that the percentage of such images on sites hosted in the United Kingdom fell from 18 percent in 1997 to .2 percent now. Still, 20 percent of all Web sites hosting images on the IWF's database were accessible at the start and the end of a six-week study period.

"One Web site, for example, was first reported in 1999, has since been reported to us 96 times and reported by us to relevant authorities a further 20 times and yet still remains available," the IWF announced in a prepared statement.

The IWF received 14,000 reports of abuse images of children in the first half of 2006, up 24 percent from 2005. The decrease in such content in the United Kingdom is likely a result of increased public awareness and reporting, Internet service providers and search engines blocking access, as well as U.K. government and police support, according to the IWF.

The group called for unified international efforts to investigate, trace and take down Web sites that host images of children being sexually abused. It also called for the end of the term child pornography," which it said could legitimize images that are permanent records of children being sexually abused.

The report showed that Japanese message boards and U.S. free hosting systems are continuing to increase the amount non-commercial images of children being sexually abused. Online photo album services grew in popularity among people posting and distributing criminal photographs and videos of children during the first half of 2006, according to the IWF.

The group runs a hotline so the public and IT professionals can anonymously report exposure to the images, no matter where they are hosted. It also takes reports of criminally obscene content and material that could incite racial hatred hosted in the United Kingdom.