If the pictures or files are recovered by someone (geek squad or whatnot) they are by definition recoverable, and therefore you were in possession of them. Child Porn possession laws require no intent. If you are in possession of it, then you are guilty.
This kind of thing is very scary for anyone who looks at buying anything used, or even reconditioned*. I consider myself pretty darn savvy on the computer security front, but that doesn't mean there's not something I might accidentally miss on used equipment. Even "full" scrubbers like boot and nuke are not completely safe, depending on security level. Obviously if "they" are processing your nuked hard drive to that point, you're probably in a lot more trouble than porn images. For most people though, who might just run a Windows reformat or something, this is very 1984.
* I posted here a couple of years ago I guess, about buying a "new" tablet on Amazon. It was offbrand Chinese. When I got it, there was already somebody else's google account set up on it. It was obviously not new, but likely a return that was reboxed without first being reset. I returned it, but if there wasn't an obvious google account on the thing, it could just as easily have had files stuck in some subfolder that I would never think of checking. So in this case, not even "new" was safe.
