Street art involves a lot of appropriation (stealing) other people’s images from the mass media, art and elsewhere. Appropriation is part of the cut and paste, Dada to hip-hop, lineage of which street art is a part. A sample, appropriated from some other work of art or design, can be used creatively to create new and original works. (I could expand on the history of sampling in music, art and literature but this is not the point.) Appropriation, sampling, homage, tribute, plagiarism, copy, whatever you want to call it, are all the various degrees of lack of authenticity and originality. And this leaves the door wide open for many kinds of abuses.
I saw a fake Banksy gangster rat on the street of Brisbane, I’m pretty sure that Banksy never went to Brisbane but if he did this would have faded in the sun by now. It has been copied from a photograph of a Banksy gangster rat but it has left out details on the ghettoblaster. This fake Banksy is different from the forgeries on sale in auction houses or on Ebay. (In April 2007 auction house Christies withdrew two alleged Banksy paintings from sale. And The Art Newspaper reported (1/10/07) that unauthorized Banksy prints with forged signatures are for sale on Ebay.) Legally it is hard to actually be a forgery when you are free and anonymously created on the street as no claims are being made about the authenticity and nobody is suffering any financial loss as a result of the deception.
Street art is frequently not just copying or sampling but plagiarizing with copies of copies of copies. (See my review of Swifty’s show and see his reply in the comments). I do not want to see another Warhol imitation or any famous high contrast black and white image reproduced in stencil-art. Copying Warhol is just repetitive and it does not make the copyist another Warhol. On a full colour sticker by Mask is a reproduction of Roy Lichtenstein’s painting of an artist and his girlfriend saying, “Oh Brad, soon all the galleries will be clamouring for your art”, only “Brad” has been replaced by “Mask”. This sucks all of irony out of Lichtenstein’s appropriation of the original comic frame. A copy of art will not alone make a work art.
There are many reasons for copying: for learning and practicing, for ironic or satirical parody, for all kinds of reasons – but copying for it’s own sake is not one of them – it is just plagiarism.