Re: What about UK?
Some info for UK readers concerning offence of "Possession of IIC" and a proven defence based on "unsolicited receipt" aka "blame the computer" that may be relevant. This quote borrowed from the Crown Prosecution Service web site. Full document at http://www.cps.gov.uk/legal/h_to_k/i...s_of_children/
This quote is not subject to amendment and absolutely does not constitute legal advice. In fact don't believe it at all. Get a lawyer if this concerns you.
In the UK, section 1 of the Protection of Children Act 1978 (PCA 1978) and section 160 of the Criminal Justice Act 1988 (CJA 1988) cover the area of CP/IIC.
Defence under CJA 1988, Subsection 160(2)(c)
The defendant must prove both
'that the photograph or pseudo-photograph was sent to him without any prior request made by him or on his behalf' and that 'he did not keep it for an unreasonable time'.
The Act does not prescribe what constitutes a 'prior request', nor does it define the parameters of 'unreasonable time'. In particular, it is not clear whether time runs from when the image was received by the computer, or when it was known by a defendant to have been received.
In R v Porter the Court of Appeal held that
"an image will only be considered in possession if the defendant had custody or control of the image at that time. If at the time of possession the image is beyond his control, then he will not possess it."
[Case (ref. Porter, R. v  EWCA Crim 560 (16 March 2006)]
Full document here http://www.cps.gov.uk/legal/h_to_k/indecent_photographs_of_children/