"Appropriation is the borrowing (or stealing , as some would insist), of an image or object from the work of another artist and incorporating it in one's own creation where its context is altered." — Sam Hunter, et al.. Modern Art: Painting, Sculpture, Architecture, Photography (Upper Saddle River, NJ: Prentiss Hall, 2004), 454.
Andy Warhol is known for his silk screens and was often accused of appropriation. Through out his career, he fought many lengthy battles over copyright. These lawsuits included photographers' work, mass produced products, and advertisements from popular culture.
The photograph of Andy Warhol, above, is shown under a Creative Commons license which grants permission to use by providing attribution to the photographer. Andy Warhol, known as the "Great Appropriator," created silk screens using recognizable images of people and objects.
Appropriation in Design:
Includes non-text sources such as graphic design, paintings, and architectural work (designs, buildings, plans, and drawings)
This includes motifs, forms, or arrangements – including but not limited to appearance, arrangement, display, or exhibition. (Drury University see HSA Plagiarism Policy: Academic and Creative Honesty section)
Modifying a design or image digitally or other processes is not enough to claim a work original, one must show a creative process. The work needs to be transformative.
"The central purpose of this investigation is to see . . . whether the new work merely “supersedes the objects” of the original creation,. . . or instead adds something new, with a further purpose or different character, altering the first with new expression, meaning, or message; it asks, in other words, whether and to what extent the new work is 'transformative.'"
Sites, Brian. "Fair Use and the New Transformative." Columbia Journal of Law & the Arts 39 (2016): 513-550.
Keep in mind, your work should "provoke critical re-evaluation of well-known pieces by presenting them in new contexts, or challenge notions of individual creativity or authenticity in art." (Oxford English Dictionary)