我正在使用Tkinter编写GUI，并希望在中显示png文件Tkiner.Label。所以我有一些这样的代码：

self.vcode.img = PhotoImage(data=open('test.png').read(), format='png')
self.vcode.config(image=self.vcode.img)

这段代码 可以在我的Linux机器上正确运行
。但是，当我在Windows计算机上运行它时，它会失败。我还在其他几台机器（包括Windows和Linux）上进行了测试，但始终失败。

追溯为：

Exception in Tkinter callback
Traceback (most recent call last):
  File "C:\Python27\lib\lib-tk\Tkinter.py", line 1486, in __call__
    return self.func(*args)
  File "C:\Documents and Settings\St\client\GUI.py", line 150, in showrbox
    SignupBox(self, self.server)
  File "C:\Documents and Settings\St\client\GUI.py", line 197, in __init__
    self.refresh_vcode()
  File "C:\Documents and Settings\St\client\GUI.py", line 203, in refresh_vcode
    self.vcode.img = PhotoImage(data=open('test.png').read(), format='png')
  File "C:\Python27\lib\lib-tk\Tkinter.py", line 3323, in __init__
    Image.__init__(self, 'photo', name, cnf, master, **kw)
  File "C:\Python27\lib\lib-tk\Tkinter.py", line 3279, in __init__
   self.tk.call(('image', 'create', imgtype, name,) + options)
TclError: image format "png" is not supported

如果删除format='png'源代码，则回溯将变为：

Exception in Tkinter callback
Traceback (most recent call last):
  File "C:\Python27\lib\lib-tk\Tkinter.py", line 1486, in __call__
    return self.func(*args)
  File "C:\Documents and Settings\St\client\GUI.py", line 150, in showrbox
    SignupBox(self, self.server)
  File "C:\Documents and Settings\St\client\GUI.py", line 197, in __init__
    self.refresh_vcode()
  File "C:\Documents and Settings\St\client\GUI.py", line 203, in refresh_vcode
    self.vcode.img = PhotoImage(data=open('test.png').read())
  File "C:\Python27\lib\lib-tk\Tkinter.py", line 3323, in __init__
    Image.__init__(self, 'photo', name, cnf, master, **kw)
  File "C:\Python27\lib\lib-tk\Tkinter.py", line 3279, in __init__
    self.tk.call(('image', 'create', imgtype, name,) + options)
TclError: couldn't recognize image data

那么，我应该怎么做才能使其支持png文件？