Tkinter: How can I update an image display?

[Terry Carroll]

I've got a small batch image-processing program (it adds the time a
digital photo was taken to the lower right of the image), and as a
feature, I wanted to show a thumbnail of each image it was being
processed.  I can't get the image to update, though.

I trimmed it down to a basic app indicating the problem and the code
is at the end of this message.  It should display the three listed
sample images, one after another.

The thing is, if I uncomment the raw_input call, it works.  But I
don't want to have to hit ENTER after each image.

At first I wondered whether maybe the image data was bad, but that
doesn't explain why it works fine with the raw_input call in place.

I've hardly played with Tkinter, so I'm probably missing something
obvious. I tried adding pack() calls for F2 and ImageLabel, and that
made no difference.

Ideas?

Here's the code:

==========================
import Tkinter as Tk
import os, sys, time
import Image, ImageTk

class MyApp:
    
    def __init__(self, root):
        """initializer for Tkinter-based application"""
        self.root=root
        F1 = Tk.Frame(self.root)
        F1.pack()       
        SelButton = Tk.Button(F1, text="Go", command=self.go)
        SelButton.pack(side="left")
        QuitButton = Tk.Button(F1, text="Quit", command=F1.quit)
        QuitButton.pack(side="left")
        F2 = Tk.Frame(self.root)
        F2.pack()
        self.ImageLabel = Tk.Label(F2)
        self.ImageLabel.pack()
        self.FilenameLabel = Tk.Label(F2)
        self.FilenameLabel.pack()


    def go(self):
        filenames = ["DSCN0184.JPG", "DSCN0185.JPG", "DSCN0186.JPG"]
        for name in filenames:
            im=Image.open(name)
            im.thumbnail((100,75))
            Tkimage = ImageTk.PhotoImage(im)
            self.ImageLabel.config(image=Tkimage)
            self.FilenameLabel.config(text=name)
            time.sleep(2)
            raw_input("Press ENTER for next...")
                
root = Tk.Tk()
myapp = MyApp(root)
root.mainloop()
==========================