Trouble displaying image with tkinter

[sj]

I am just learning to use Tkinter and am having problems displaying image
files. I am able to display an image using tutorials (such as
http://www.daniweb.com/code/snippet296.html) But when I try my own code all
I get is an empty widget. What is wrong with the following program?




from Tkinter import *

class Foo(Frame):

    def __init__(self,master=None):
        Frame.__init__(self,master)
        self.pack()
        self.createWidgets()



    def createWidgets(self):

        self.qbutton = Button(self)
        self.qbutton["text"] = "Quit"
        self.qbutton["command"] = self.quit
        self.qbutton.pack(side = "top")

        idata =
PhotoImage(file="/home/sj/documents/projects/xaed/images/cat_001.gif")

        canvas = Canvas(width=300,height=200)
        canvas.pack(side="top",fill=BOTH,expand=YES)
        canvas.create_image(50,10,image=idata,anchor=NW)

        ## lab = Label(self,image=idata)
        ## lab.pack(side=TOP)
        

root = Tk()
app = Foo(root)
app.mainloop()
#app.destroy()