Just as a feature among others, dealing with images using PyMuPDF is easy. It may avoid using other graphics packages like PIL/Pillow in many cases. Notwithstanding that interfacing with Pillow is almost trivial.

The general scheme is as simple as follows:

import fitz
# ...
pix = fitz.Pixmap("input.xxx") # input.xxx: a file in any of the supported input formats
pix.writeImage("output.yyy") # yyy is any of the supported output formats

1. The argument of fitz.Pixmap(arg) can be a file or a bytes or io.BytesIO object containing a file image
2. Instead of creating an output file like above, you can also create a bytes object via pix.getImageData("yyy") and pass this around.
3. As a matter of course, input and output formats must be compatible in terms of colorspaces and transparency. The Pixmap class has batteries included for cases, where this is not so.
4. Since v1.14.6, pix.writeImage() no longer requires an extra format parameter: the format is inferred from the filename's extension.

import fitz
pix = fitz.Pixmap("myfamily.jpg")
pix.writeImage("myfamily.psd")

from PIL import Image
import fitz
pix = fitz.Pixmap(...)
img = Image.frombytes("RGB", [pix.width, pix.height], pix.samples)
img.save("output.jpg", "JPEG")

import fitz
if str is bytes: # this is Python 2!
 import Tkinter as tk
else: # Python 3 or later!
 import tkinter as tk
pix = fitz.Pixmap("input.jpg")
tkimg = tk.PhotoImage(data=pix.getImageData("ppm")) # PPM is among the tk-supported formats