Why does my Tkinter GIF image disappear when inside a class?

[midtoad]

I'm trying to display a GIF image in a label as the central area to a
Tkinter GUI.   The image does not appear, though a space is made for it. 
Why is this so?

I notice that I can display a GIF image in the central area of a simple
menu-bar app as shown below in the first code sample. But, when I set up my
app with a class, as shown below in the second code sample, the image
disappears.   

How can I correct this? I'm sure the answer would jump out at me if I
thought more clearly about it...

thanks
S

---
#basicmenu.py : displays GIF image


from Tkinter import *


def callback(text):
    print "called the callback!: "+text

root = Tk()

# create a menu
menu = Menu(root)
root.config(menu=menu)

filemenu = Menu(menu)
menu.add_cascade(label="File", menu=filemenu)
filemenu.add_command(label="New", command=callback('new'))
filemenu.add_command(label="Open...", command=callback('open'))
filemenu.add_separator()
filemenu.add_command(label="Exit", command=callback('exit'))

helpmenu = Menu(menu)
menu.add_cascade(label="Help", menu=helpmenu)
helpmenu.add_command(label="About...", command=callback('about'))

img00 = PhotoImage(format='gif',data=
             'R0lGODlhKwAQAJEAACWgA/3bYYNOGgAAACwAAAAAKwAQAAACfIyPqcsrD2M0'
            +'oAJqa8h29yAkITiG3HWmKWiUrdtpseZdtcfmJSyjvf2Z5Q671u0wA9I+RtLj'
            +'ZcwgfxglTTchjqS34JUrCUMQySOzih07Tb62eeneqSfU8vsmf65xZa8S/zI3'
            +'dlLD5deRl1dlxdT4MYIA2TBJuSZ2iZkZVgAAOw==')

newLabel = Label(root,image=img00)
t = str(img00.width()) + ' wide x ' + str(img00.height()) + ' high'
newLabel.pack()
Label(root,text='The image is\n'+t).pack()

mainloop()
---
#basicmenu2gifobj.py : doesn't display image

from Tkinter import *

class gifMenu:
    def __init__(self, parent):

        # create a menu
        menu = Menu(parent)
        parent.config(menu=menu)

        filemenu = Menu(menu)
        menu.add_cascade(label="File", menu=filemenu)
        filemenu.add_command(label="New", command=callback('new'))
        filemenu.add_command(label="Open...", command=callback('open'))
        filemenu.add_separator()
        filemenu.add_command(label="Exit", command=callback('exit'))

        helpmenu = Menu(menu)
        menu.add_cascade(label="Help", menu=helpmenu)
        helpmenu.add_command(label="About...", command=callback('about'))

        img00 = PhotoImage(format='gif',data=
              'R0lGODlhKwAQAJEAACWgA/3bYYNOGgAAACwAAAAAKwAQAAACfIyPqcsrD2M0'
            +'oAJqa8h29yAkITiG3HWmKWiUrdtpseZdtcfmJSyjvf2Z5Q671u0wA9I+RtLj'
            +'ZcwgfxglTTchjqS34JUrCUMQySOzih07Tb62eeneqSfU8vsmf65xZa8S/zI3'
            +'dlLD5deRl1dlxdT4MYIA2TBJuSZ2iZkZVgAAOw==')

        newLabel = Label(parent,image=img00)
        t = str(img00.width()) + ' wide x ' + str(img00.height()) + ' high'
        newLabel.pack()
        Label(parent,text='The image is\n'+t).pack()

class callback:
    def __init__(self, text):
        self.text = text
    def __call__(self):
        print 'Command is: ',self.text

######################################################################

# Create GUI in root window for testing.
if __name__ == '__main__':
    title='Menu test with GIF'
    root = Tk()
    #Pmw.initialise(root)
    root.title(title)

    #exitButton = Tkinter.Button(root, text = 'Exit', command =
root.destroy)
    #exitButton.pack(side = 'bottom')
    gifMenu = gifMenu(root)


    root.mainloop()