It's been my experience that the people who share/photocopy textbooks aren't doing it to screw publishers, they do it because they cannot afford to buy the book themselves. It is a lot of extra work to pirate textbooks this way; I doubt anyone would bother without a good reason.

Once again, it seems like all it's going to do is make legitimate customers jump through hoops, while the pirates find loopholes or simply fail... neither of which results in additional revenue for publishers.