HAMILTON -- At what point does someone actually possess the pornographic image on a computer screen?
Police say possession occurs when you save an image on the computer's hard drive or a diskette, but experts say advances in software and computer technology make the question more complicated than that.
Jeffrey Shallit, a University of Waterloo computer science professor, says that depending on the computer and software used, "even when you just visit a site, something is downloaded to the memory of your machine."
Most people have no idea what the software on their computers can do, Shallit said.
"Whatever you see on the screen is in memory; every pixel of the screen is just a portion of the memory, essentially", Shallit said.
Nicholas Solntseff, a McMaster University computer science professor, says current software features a memory cache, a temporary storage area on the computer's hard drive. The cache consists of material viewed and then automatically downloaded onto the hard drive, whether the user wants it or not.
This memory cache can be disabled, but if it isn't, material is automatically caught and stored on the hard drive.
"Having a cache of several megabytes is useful because it saves time, he said. If the downloaded material is to be used again, it eliminates the tedious process of relocating the site.
The cache is relatively small, though, and files stored in it are constantly being replaced by new files as the computer is used.
"It's quite possible to look at stuff, then go away and think it's completely gone, but it's actually still there somewhere, and a person who knows how might be able to retrieve it", Shallit said.
Automatic electronic mailing lists further complicate the issue.
"Suppose you subscribe to an automatic mailing list, and suppose some guy decides to send out a pornographic picture in some well-known format to everyone on the mailing list", Shallit said. "Well, say you're away for a few weeks, and you come back an there's all this stuff in your mailbox. You had no knowledge of it, but it's on your hard drive."
If you installed the software that captured an illegal image you don't want and weren't even looking for, is it still possession?
And what about network backups, where a backup computer automatically copies everything viewed on a primary computer? Deleting primary files won't affect backup files.
"The question is when do you physically possess it, and I don't think that's a question which has been answered in any definitive way by any court anywhere", Shallit said. "The simple answer is that software may make temporary copies of things without your knowledge, and those copies may reside either in memory or on the computer's disk. Most software gives you some option to decide, but the average user simply may not know whether copies have been saved or not."
In some cases, users pull information directly from one of the desired computers. To each certain desired computers a user may have to travel through other computers.
If a user is not at an institution with a direct connection to a desired computer that is part of the Internet, that person will dial into an intermediary computer, known as a service provider.