Conventional wisdom (and the Electronic Frontier Foundation) says that
an unauthorized screenshot is an infringement. That said, the use of
screenshots rarely triggers a complaint because either: (1) the
copyright owners don’t want to complain about something that promotes
their company -- for example, an online tutorial about using Microsoft
Word, or a book about starting an eBay business, or (2) the copyright
owners believe the use is likely to be excused as a fair use. Although
issues don’t often arise, occasionally copyright owners do complain --
for example, Apple complained about prerelease screenshots of the
iPhone. Some sites place limits on your use of screenshots in their
user agreements.