Some excepts from the reasons.
From the majority reasons of Fish J (McLachlin C.J. and Binnie, Abella JJ concurring):
[1] This case concerns the right of everyone in Canada, including the appellant, to be secure against unreasonable search and seizure. And it relates, more particularly, to the search and seizure of personal computers.[2] It is difficult to imagine a search more intrusive, extensive, or invasive of one’s privacy than the search and seizure of a personal computer.
[3] First, police officers enter your home, take possession of your computer, and carry it off for examination in a place unknown and inaccessible to you. There, without supervision or constraint, they scour the entire contents of your hard drive: your emails sent and received; accompanying attachments; your personal notes and correspondence; your meetings and appointments; your medical and financial records; and all other saved documents that you have downloaded, copied, scanned, or created. The police scrutinize as well the electronic roadmap of your cybernetic peregrinations, where you have been and what you appear to have seen on the Internet — generally by design, but sometimes by accident.
[4] That is precisely the kind of search that was authorized in this case. ...
The majority held that the search warrant was improperly obtained, the search was illegal, and the evidence obtained as a result of the search was to be excluded under s.24(2) of the Charter.
[13] The threshold question on this appeal is whether the justice of the peace who issued the search warrant acted on reasonable and probable grounds, as required under both the Criminal Code and the Charter. To answer that question, it is necessary to first understand when one may properly be said to “possess” an image in a computer, within the meaning of s. 163.1 of the Criminal Code.
[14] In my view, merely viewing in a Web browser an image stored in a remote location on the Internet does not establish the level of control necessary to find possession. Possession of illegal images requires possession of the underlying data files in some way. Simply viewing images online constitutes the separate crime of accessing child pornography, created by Parliament in s. 163.1(4.1) of the Criminal Code.
[34] For the sake of greater clarity, I turn now to consider how this understanding of possession applies to files in an Internet cache (that is, copies of files automatically stored on the hard drive by a Web browser).
[36] On my view of possession, the automatic caching of a file to the hard drive does not, without more, constitute possession. While the cached file might be in a “place” over which the computer user has control, in order to establish possession, it is necessary to satisfy mens rea or fault requirements as well. Thus, it must be shown that the file was knowingly stored and retained through the cache.
[37] In the present case, the charge is not based on the appellant using his cache to possess child pornography. It is hardly surprising as most computer users are unaware of the contents of their cache, how it operates, or even its existence. Absent that awareness, they lack the mental or fault element essential to a finding that they culpably possess the images in their cache. Having said that, there may be rare cases where the cache is knowingly used as a location to store copies of image files with the intent to retain possession of them through the cache.
[38] Justice Deschamps has advanced a more expansive conception of possession, under which simply viewing an image might, in some circumstances at least, constitute possession. As I will presently explain, even if one were to adopt my colleague’s view, the ITO in this case fails to establish reasonable and probable grounds for the impugned search of the appellant’s computer.
[105] As I mentioned at the outset, it is difficult to imagine a more intrusive invasion of privacy than the search of one’s home and personal computer. Computers often contain our most intimate correspondence. They contain the details of our financial, medical, and personal situations. They even reveal our specific interests, likes, and propensities, recording in the browsing history and cache files the information we seek out and read, watch, or listen to on the Internet.
[106] It is therefore difficult to conceive a s. 8 breach with a greater impact on the Charter-protected privacy interests of the accused than occurred in this case.
from the dissent by Deschamps J: (Charron and Rothstein JJ concurring)
[Reminder - emphasis added by me in para. 144][114] Internet and computer technologies have brought about tremendous changes in our lives. They facilitate the communication of information and the exchange of material of all kinds and forms, with both legal and illegal content, and in infinite quantities. No one can be unaware today that these technologies have accelerated the proliferation of child pornography because they make it easier to produce, distribute and access material in partial anonymity: …
[140] This case does not require the Court to elaborate on the distinctions between accessing and possession of prohibited material. Suffice it to say that the question before us turns not on whether the accused has merely viewed the material, but on whether evidence of control over the material could be found in the computer that was to be searched. Accessing does not necessarily require control, and possession does not necessarily require viewing. Therefore, for the purposes of the offence of possession, viewing might be one way to prove knowledge of the content, but it is not the only way. Similarly, viewing might be one way to prove control, but it may not be sufficient — the circumstances in which the material was viewed would need to be proven. Control, not viewing, is the defining element of possession.
[141] Therefore, even if an accused does not actually download offending material, possession is established if the accused has control over the material for his or her use or benefit or for that of someone else. The record does not indicate that the reviewing judge was provided any evidence on caches. However, there is now abundant legal literature in which the authors have discussed caches, temporary Internet files, and deleted material that can be retrieved, all of which may, under relevant circumstances, constitute evidence of possession. The degree of control might be established on the basis, for example, of the displaying of the images and the ability to select, cut, enlarge, print, forward or share images: see G. Marin, “Possession of Child Pornography: Should You Be Convicted When the Computer Cache Does the Saving for You?” (2008), 60 Fla. L. Rev. 1205, at p. 1212; T. E. Howard, “Don’t Cache Out your Case: Prosecuting Child Pornography Possession Laws Based on Images Located in Temporary Internet Files” (2004), 19 Berkeley Tech. L.J. 1227; Akdeniz, at pp. 32-58 and 150-52; P. H. Luehr, “Real Evidence, Virtual Crimes: The Role of Computer Forensic Experts” (2005-2006), 20 Crim. Just. 14; R. Michaels, “Criminal Law — The Insufficiency of Possession in Prohibition of Child Pornography Statutes: Why Viewing a Crime Scene Should Be Criminal” (2008), 30 W. New Eng. L. Rev. 817.
[144] The definition of possession advanced by the appellant and adopted by my colleague Fish J. could freeze possession in time and limit it to certain modes of storage and media. As a practical matter, there is little difference between exercising control over the hard drive of a computer while on the premises where the computer is located and exercising control over of the on-line space of a Web-based hosted service. Moreover, if, to bring a cache into the scope of possession, the accused were required to have knowledge of how caches work, this would require proof of intent or technical savvy on the part of the accused. As I mentioned above, the requisite mens rea will be established at trial if it is shown that the accused willingly took control of the object with full knowledge of its character. In light of the inevitability of technological change, it is important not to needlessly handcuff the courts to a concept of possession that is limited to certain technologies or to current-day computer practices. Control has been the defining feature of possession, not the possibility of finding data files on a hard drive. To adopt downloading as the threshold criterion would be to take a formalistic approach rather than drawing a principled distinction between access and possession. The classical approach to possession, rooted in control, therefore remains the most reliable one. It is the one that is most readily adapted to technological developments and it will not require courts to hear detailed forensic evidence of technological advances on an ongoing basis just to keep up with the times.
[145] The rules applicable to the authorization of a search do not change where the possession of electronic material is in issue. I would add that in view of the amount of material that can be found on the Internet, it is all the more important not to unduly restrict the concept of control: printing, enlarging and sharing are all actions which do not require downloading but may be evidence of control. Moreover, to limit possession to material downloaded to the computer of the accused would be to render constructive possession all but inapplicable in the context of the Internet. As I mentioned above, evidence of possession can take many forms and, although it must show control, is not limited to actual possession of the material.
