You're in a grey area there. There is a lot of pressure these days to broaden the definition of cp to include everything that looks erotic involving people under 18. England is the worst place for this grade-inflation, but it's also going on elsewhere. 'Temporary internet files' that are automatically made by your browser whenever at you look at online images, including thumbnails (especially if you use Internet Explorer) are certainly sufficient for a charge to be laid against you if the images found are considered illegal. In fact, temporary internet files like that are one of the main things law enforcement goes looking for.

There WAS a case in Europe where a politician who was known to like barely-legal boys threw out his laptop in the regular garbage (curbside), and then adventurous people snapped it up and took it off to look for dirt... they found a few cp thumbnails in the temporary internet files, and the politician was charged. He claimed in his defense that he had never deliberately looked at cp but had had some popups like that while looking at legal sites, and had closed the windows immediately, with no idea that temp files would be stored. Amazingly, the judge believed him and he was acquitted. Actually, he was being accurate; in the early 2000's, part of the advertising gimmick for barely-legal porn sites was to advertise on thumbnail broadsheets apparently offering free promo pics. These sheets, though, used images that, instead of leading to free porn, led to a 'dialer' program randomly producing another ad, or a similar broadsheet, or, if you were unlucky, a trojan, a virus, or a popup with cp thumbnails in it. So all the avid free porn collectors would occasionally see a cp popup. It was a really Russian roulette (the sites were mostly Russian). This was widely discussed, needless to say, but it wasn't something every judge would know about. So the fellow got lucky.

I just don't know if a U.S. or British judge would buy the 'coincidental catch' argument that won it for the Euro politician.

If you're not sure, then close the page right away. Use your ccleaner to clean away the temporary internet files. Then, if you want to be extra careful, you can get the free fileshredder from www.fileshredder.org and use its "shred free disk space" function to wipe out any traces and remains of previous files that you might have deleted (which, on the computer, means unhooked from the file index so that they're no longer protected from being over-written), but not completely wiped out.