Graffiti Drawings By Banksy

Asked about his technique, Banksy said:
“I use whatever it takes. Sometimes that just means drawing a moustache on a girl's face on some billboard, sometimes that means sweating for days over an intricate drawing. Efficiency is the key.”
Stencils are traditionally hand drawn or printed onto sheets acetate or card, before being cut out by hand. Because the secretive nature Banksy's work and identity, it is uncertain what techniques he uses to generate the images in his stencils, though it is assumed he uses computers for some images due to the photocopy nature much his work.
He mentions in his book, Wall and Piece, that as he was starting to do graffiti, he was always too slow and was either caught or could never finish the art in the one sitting. So he devised a series intricate stencils to minimise time and overlapping the colour.