First paragraph:
More than 50% of online images of child abuse reported to an internet watchdog can be traced to the US, a report says.
Second paragraph:
Investigations by the Internet Watch Foundation (IWF) found nearly 2,500 US sites containing illegal images.
Put 'em together, and what do you get?
2,500 US sites = 50% of all sites that contain images of child abuse ... because, if a site is reported to the organization and does *not* contain images of child abuse, then it is not included in the sites containing "online images of child abuse reported" to the organization, because it is not a site that contains online images of child abuse.
It even makes this clear:
In the first six months of this year the IWF received more than 14,000 reports of suspected websites, a 24% increase on the first six months of 2005. ... Of the reports, nearly 5,000 contained images of child abuse. Of these nearly 2,500 were traced to the US and more than 730 to Russia.
It also points out:
The IWF, which is based in the UK, said that the reason why the US hosted the majority of illegal content was because the country has the most ISPs and the most web traffic in the world.
Of course.
One might say, however, that on that basis the US also has the most responsibility for doing something about the problem.
The organization reports that some sites remain accessible for years despite being reported to appropriate authorities. The article then also reports proposals by such authorities for doing something about it.
It's entirely possible that some sites are reported to the organization out of spite, for instance. There doesn't seem to be any reason to think that the sites that the organization refers to as actually containing such images include any of them.