If you need to work with other file formats, the Python Imaging Library (PIL) contains classes that lets you load images in over 30 formats, and convert them to Tkinter-compatible image objects:
from PIL import Image, ImageTk
image = Image.open("lenna.jpg")
photo = ImageTk.PhotoImage(image)
You can use a PhotoImage instance everywhere Tkinter accepts an image object. An example:
label = Label(image=photo)
label.image = photo # keep a reference!
label.pack()
You must keep a reference to the image object in your Python program, either by storing it in a global variable, or by attaching it to another object.