title: image doesn't show up on canvas output
body: <p>I am trying to simply get some image on canvas, but even though I don't get any errors, my canvas stays white, no picture shows up. I know it will be some stupid misteak, but I can't find it.</p>
  
  <pre><code>def obrazek():
      mesic = tkinter.PhotoImage(file="moon-0.gif")
      canvas.create_image(700, 500, image = mesic)
  
  rodic = tkinter.Tk()
  rodic.title(u"Slunce a Měsíc")
  rodic.geometry("+1000+300")
  canvas = tkinter.Canvas(rodic, width=1400, height=800,)
  canvas.pack()
  obrazek()
  tkinter.mainloop()
  </code></pre>
  
  <p>Output is whitescreen.</p>