At The Smoking Gun:

Federal prosecutors want Shepard Fairey, the artist who created the Barack Obama “Hope” poster, to serve time in prison following his misdemeanor conviction for destroying and fabricating documents in connection with a civil lawsuit over the iconic campaign image. . . .

Fairey . . . has admitted destroying electronic records and creating fake documents in an effort to thwart a copyright lawsuit brought by the Associated Press, which contended that Fairey had based the “Hope” image on a photo taken by an AP lensman.

Plagiarism is an "act or instance of using or closely imitating the language and thoughts of another author without authorization and the representation of that author's work as one's own, as by not crediting the original author," states Dictionary.com. This would include "a piece of writing or other work reflecting such unauthorized use or imitation."

Note, however, one can plagiarize even if there is an under-the-table "authorization" to allow it (sometimes protected by a contract's "nondisclosure clause"). Ghostwriting, for example, is often preceded by a legal agreement in which a "big name" pretend author agrees to take credit for work in fact authored by the "ghost." 

The true authorship of the book is hidden from the reading public, for any number of rationalizations. Both the "author" and real writer (and their lawyers and organizations and publishers) have thereby agreed to deceive and manipulate to achieve some desired end (book sales, image enhancement, influence, etc.).

Being known as an "author," or having a list of 20 or 30 books he or she has "written," can do wonders for one's speaking fees, the status of one's organization, the rehabilitation of one's besmirched image, and the "legacy" you've carefully crafted for years so that all remains well when you're dead and gone.

It's all "nice and legal," but unethical. Two wrongs do not make a right. Even if "legal." Even if agreed to by consenting adults. This is true even if some big "Christian" celebrity's name (often PRed as a "spiritual giant") is stuck on the front of the book. Or on the front of 30 books.

Related
Francis Schaeffer -- "The Central Problem of Our Age"
Oxford, Cambridge, Plagiarism, and Christian Worldview
Francis Schaeffer: A Student's Appreciation of a Distinct Approach