Last night I was attempting to download some Family Guy cartoons and got a heap of porn in the search results. I used the filter and ran the search again. It blocked out most of the porn but a couple snuck through.
From what I have found most of the porn have fairly descriptive names so you'd have to be pretty unlucky to download a child porn movie inadvertantly.
If it does happen my advice would be to report it immediately to the authorities, They may not be able to catch the perpretrators BUT; There will be a record of your complaint and if, by chance the authorities detect a deleted child porn movie on your hard drive you will be covered.
I wonder, though. How would they know where to look?
They would have to have some reason to be searching through your hard drive for deleted images, wouldn't they?
My best advice is to avoid ALL porn completely, let's face it, it's all pretty tacky and puerile. Mostly harmless but totally unnecessary, like looking into the display window of a butcher shop really! Seen one you've seen them all and shouldn't we be directing our attention to more cerebral, productive forms of entertainment