Appropriation

Appropriation artists intentionally copy images to take possession of them in their art. They are not stealing. They are not passing off these images as their own. Appropriation artists want the viewer to identify the images they copy, and they hope that the viewer will bring all of his/her original associations with the image to the artist's new context, be it a painting, a sculpture, a collage, a combine or an entire installation.
The intentional borrowing of an image for this new context is called recontextualization. It helps the artist comment on the image's original meaning and the viewer's association with the original image or the real thing. For example Andy Warhol's Campbell's Soup cans series. These images are appropriated. He copied the original labels exactly, but filled up the picture plane with their iconic appearance. Unlike other garden-variety still-life’s, these works look like portraits of a soup can. The brand is the image's identity.

Warhol isolated the image of these products to stimulate product recognition (just like in advertising) and stir up associations with the idea of Campbell's soup. He also tapped into a whole bunch of other associations, such as consumerism, commercialism, big business, fast food, middle class values, and food representing love. As an appropriated image, these specific soup labels could resonate with meaning (like a stone tossed into a pond) and so much more. Warhol's use of popular imagery became part of the Pop art movement.
All Appropriation Art is not just Pop Art, though. Artist Sherry Levine's After Walker Evans (1981) is a photograph of a Walker Evans photograph. She is challenging the concept of ownership, if she photographed the photograph, whose photograph was it, really? And she is addressing the power of male artists as Sherry Levine is a feminist artist.

http://www.tate.org.uk/collections/glossary/definition.jsp?entryId=23
http://weblog.delacour.net/photography/appropriation-art-and-walker-evans/