title: NameError: name 'PhotoImage' is not defined, dont know how to add image
body: <p>I'm trying to add a background image to the window but I can't. I tried almost every way I know...</p>
  
  <pre><code>class main:
      def __init__(self):
          global lol
          self.rip = tk.Tk()
          self.f2 = tk.Frame(self.rip)
          self.f2.grid(column=0, row=0, sticky=("nwes"))
          self.f2.columnconfigure(0, weight=1)
          self.f2.rowconfigure(0, weight=1)
          self.c1=tk.Label(self.f2, text="feet to meter or meter to feet?")
          self.c1.grid(row=0, column=0)
          self.c2=tk.Label(self.f2, text='type "ft" for feet to meter, type "m" for meter to feet')
          self.c2.grid(row=1, column=0)
          lol = tk.StringVar()
          self.choice = tk.Entry(self.f2, width=7, textvariable=lol)
          self.choice.grid(row=2, column=0)
          self.b1=tk.Button(self.f2, text="Confirm", command=choose)
          self.b1.grid(row=3, column=0)
          self.bg = PhotoImage(file="bgmain.gif")
          tk.Label(self,image=self.bg).pack()
          self.pack(side="top")
  </code></pre>
  
  <p>The error message says:<br>
  <code>NameError: name 'PhotoImage' is not defined</code>.<br>
  How can <code>PhotoImage</code> not be defined???</p>