PIL provides a show method which attempts to detect your OS and choose an
appropriate viewer. On Unix it tries calling the imagemagick command display
or xv. On Macs it uses open, on Windows it uses... something else.
If it can't find an appropriate viewer, ImageShow._viewers will be an empty list.
On Raspbian, you'll need to install an image viewer such as display, xv or fim. (Note a search on the web will show that there are many image viewers available.) Then
you can tell PIL to use it by specifying the command parameter:
image.show(command='fim')
To display an image in Tkinter, you could use something like:
from PIL import Image, ImageTk
import tkinter as tk
root = tk.Tk()
img = Image.open("image.gif")
tkimage = ImageTk.PhotoImage(img)
tk.Label(root, image=tkimage).pack()
root.mainloop()