code: def round_corner(radius, fill):
      
      corner = Image.new('L', (radius, radius), 0)  # (0, 0, 0, 0))
      draw = ImageDraw.Draw(corner)
      draw.pieslice((0, 0, radius * 2, radius * 2), 180, 270, fill=fill)
      return corner
docs: Draw a round corner