"In a 1994 case, the Supreme Court emphasized this first factor as being an important indicator of fair use. At issue is whether the material has been used to help create something new or merely copied verbatim into another work.
When taking portions of copyrighted work, ask yourself the following questions:
In a parody, for example, the parodist transforms the original by holding it up to ridicule. At the same time, a work does not become a parody simply because the author models characters after those found in a famous work."
From Stanford University
The Fair Use doctrine is recognized under U.S. copyright law as an individual right and allows certain uses of copyright protected material without first obtaining permission from the copyright holder. It is intended to serve the public good by allowing use of copyright protected materials for comedy, parody, news reporting, research and education. There are four criteria that are considered when determining fair use: the purpose or character of the use, the nature of the use, the amount used, and the effect on the market.
In discussing the making of art, artists "Artists may invoke fair use to incorporate copyrighted material into new artworks in any medium, subject to certain limitations" (College Art Association).
The use of a preexisting work, whether in part or in whole, should be justified by the artistic objective, and artists who deliberately repurpose copyrighted works should be prepared to explain their rationales both for doing so and for the extent of their uses.
Artists should avoid suggesting that incorporated elements are original to them, unless that suggestion is integral to the meaning of the new work.
When copying another’s work, an artist should cite the source, whether in the new work or elsewhere (by means such as labeling or embedding), unless there is an articulable aesthetic basis for not doing so.
Generally speaking, within Fair Use the 10% rule is used. An Artist can use 10% of an existing copyrighted work under the guide lines of fair use. However, this is not always the case, and in using that work, the creator must ensure that their new work is transformative enough to warrant the use.
What it comes down to: Enacting Fair Use is always a gamble because there is no hard and fast rule regarding what is and is not Fair Use. The only body that can absolutely rule that the use of a copyrighted material is fair is the courts.