title: Why it shows blank instead of picture in my Tkinter program?
body: <p>I want to use Tkinter to display all the pictures in a specific directory, so I firstly code to show all the pictures from a given list</p>
  
  <p>The code is:</p>
  
  <pre><code>import os
  
  from Tkinter import *
  from PIL import Image, ImageTk
  
  class Application(Frame):
      def add_pic_panel(self, pic):
          img = ImageTk.PhotoImage(Image.open(pic))
          label = Label(root, image = img)
          print label
          return label
  
      def create_gui(self):
          pics = ['1.jpg', '2.jpg']
          for pic in pics:
              self.add_pic_panel(pic)
          pass
  
      def __init__(self, master=None):
          Frame.__init__(self, master)
          self.pack()
          self.create_gui()
  
  root = Tk()
  app = Application(master=root)
  app.mainloop()
  root.destroy()
  </code></pre>
  
  <p>Environment: Mac OS 10.9, Python 2.7.5
  How could I display all the pictures in the list?</p>