Copyright law in the USA may be more liberal about scanning than other jurisdictions (see the parallel comment from gpm), which expressly regulate the amount of copying of material you do not own as an item.

The jurisdictions I'm familiar with all give vague fair use/fair dealing exceptions which would cover some but not all copying (including scanning) with less than clear boundaries.

I'd be interested to know if you knew of one with bright line rules delineating what is and isn't allowed.