title: Tkinter Label does not show Image
body: <p>I'm trying to learn some tkinter. I can't get tkinter to display an icon. I don't know where it goes wrong. It does not produce any error and it respects the size of the image, but it's invisible. Everything I found online tells to add a second reference to prevent garbage collection from python, but somehow this did not the trick. 
  Here is the part of my code that goes wrong:</p>
  
  <pre><code>from Tkinter import *
  from PIL import Image, ImageTk
  
  class GUI:
  
      def __init__(self, master):
  
          frame = Frame(master)
          frame.pack()
  
          #status bar
          self.bar = Frame(root, relief=RIDGE, borderwidth=5)
          self.bar.pack(side=TOP)
  
          self.iconPath = 'data/icons/size.png'
          self.icon = ImageTk.PhotoImage(Image.open(self.iconPath))
          self.icon_size = Label(self.bar, image = self.icon)
          self.icon_size.pack(side=LEFT)
  
  root = Tk()
  
  
  app = GUI(root)
  
  root.mainloop()
  </code></pre>