That is decided by “fair use”. In legal terms: “Fair use was created to allow use of copyright (sic) material for socially valuable purposes such as commentary, parody, news reporting, education and the like, without permission of the copyright holder.”
In plain English: “fair use” allows people or companies to use those materials (text, images, photos, etc.) without it being an infringement of copyright. In such cases, the owners of those copyrighted work must allow their work to be used by designers, bloggers, content writers, journalists, teachers, comedians, etc. without any legal or financial obligations. It must be noted that the burden of proof is the one using it; not the owner of the work. (In legalese: “affirmative defense”)
The reason for “fair use” is to allow reasonable and limited use of the copyrighted work. A journalist is allowed to quote from a newly published novel in the review it. A comedian can quote from copyrighted text, use a copyrighted picture or photo or directly quote a celebrity to make fun of them. Teachers and professors can use passages of copyrighted works to explain something to their students or to make a point.
As a rule of thumb, using text under “fair use” normally consists of using a small part of the copyrighted work and includes crediting the author (with a link to the source/author’s website). Fair use is for non–commercial purposes.
The criteria of what is “fair use” are defined in the opinion of the famous Joseph Story in Folsom v. Marsh, 9 F.Cas. 342 (1841). This so-called Four Factor test consist of:
1. the purpose and character of the use (non-commercial, educational, parody or non-profit)
2. the nature of the copyrighted work
3. the amount and substantiality of the portion used of the copyrighted work
4. the effect of the market use / market value of the copyrighted work
