How to show PIL images on the screen?

I tested this and it works fine for me:

from PIL import Image
im = Image.open('image.jpg')
im.show()

From near the beginning of the PIL Tutorial:

Once you have an instance of the Image class, you can use the methods defined by this class to process and manipulate the image. For example, let's display the image we just loaded:

     >>> im.show()

Update:

Nowadays the Image.show() method is formally documented in the Pillow fork of PIL along with an explanation of how it's implemented on different OSs.