...text quotes are governed by the concept of 'fair use' ....fair use is generally reckoned to be pretty healthy. ...a 'parody' of a copyrighted work is considered “transformative” and thus fair. Another example - in 2002 a US court enabled image search engines to expand beyond simple Web text searching into images and video because “thumbnails” of digital photographs are considered to be fair uses. Thumbnails, the court ruled, do not replace the original in the marketplace.
As far as publishing is concerned, some publishers demand that every quote — no matter how short or for what purpose — be cleared with specific permission, which is extremely cumbersome.... There is a lot of confusion about fair use ...you might be familiar with the "20 percent” rule - use of a work before the use becomes unfair, or the "forty-word rule” for long quotes of text. Neither rule exists. Fair use is intentionally vague. It is meant for judges to apply, case by case. ... ..
http://fairuse.stanford.edu/Copyrigh...view/chapter9/