A random person came along and posted a horrible and suggestive comment on one of the photos. She was horrified, and googling the username left (the only ID available) she came across another website where she found holiday photos and other innocent pictures of children, again with suggestive and disturbing comments. Looking further, she decided that although some of the photos had simply been stolen, some of them seemed to have been posed.
She was disturbed by this, and reported both the comment and the website to the police. Here's the bit that alarmed me though : the police turned up on her doorstep, took her laptop away, and left her with the impression that her name would end up on the sex offenders register.
They did come back later to supply a receipt and clarify that she was not currently considered a suspect, but honestly: if the police want people to report this sort of thing, is this the way to go about it? She's a married woman with a little child who is transparently alarmed by the idea that the Internet Has Nasty People On It: if she gets treated this way, then I can't help feeling that if a single bloke accidentally stumbled across something dodgy while perhaps doing something like surfing perfectly legal adult material, then I'd completely understand why he might choose to move on his way looking nonchalant rather than risk reporting it.