from Tkinter import *
import PIL.Image, PIL.ImageTk
EDGE = [-6, -4, -2][1]
class Root(Tk):
  def __init__(self):
    Tk.__init__(self)
    self.p = PIL.Image.open('hoge.gif')
    self.i = PIL.ImageTk.PhotoImage(self.p)
    self.l = Label(self, image=self.i, relief=RAISED)
    self.l.pack(expand=True, fill=BOTH)
    self.l.bind('<Configure>', self.change_size)
  def change_size(self, ev):
    (w, h) = (ev.width + EDGE, ev.height + EDGE)
    self.i = PIL.ImageTk.PhotoImage(self.p.resize((w, h)))
    self.l.configure(image=self.i)
    print 'resized %d %d' % (w, h)
Root().mainloop()

縁の幅を間違うと勝手にサイズが・・・orz