Tkinter buttons with image ?

[kowald at molgen.mpg.de]

Hi everybody,

I'm just getting into Tkinter and try to create a button that displays an image
instead of text. I do something like: 

>tmp = PhotoImage(file='start.gif')
>buttonStart = Button(frameWb,image=tmp,command=root.quit)

The button now displays a blank (grey) area of the size of the image, but as I
said, it is blank :-(. 

Any idea what I'm doing wrong ?
I'm using Python2.3

Many thanks,

             Axel