Appropriation: Art Making?

In the visual arts, to appropriate means to adopt, borrow, recycle or sample aspects of man-made visual culture.

I think this process is a valid form of art making because it isn't just copying, it is creating an alternative meaning and using objects or images to convey a point. The process has a subject matter and can be altered in various ways therefor making it art. It is all about speaking through visual language. As long as the appropriating artist isn't claiming the image to be an original or their own than they can usually dodge copyright claims.