'`str_` is the string used to generate the identicon.
`background` is the background of the identicon.'

def __init__(self, str_, background='#fafbfc'):

    w = h = ((BORDER_SIZE * 2) + (SQUARE_SIZE * GRID_SIZE))
    self.image = Image.new('RGB', (w, h), background)
    self.draw = ImageDraw.Draw(self.image)
    self.hash = self.digest(str_)
