This is a Python script to walk a directory tree, renaming .jpg and .JPG files. It was written for a client who had a directory containing multiple directories, each containing zero or more (up to 100) image files. Most of the images were named <abitrary name 1>.jpg or <arbitrary name 2>.JPG.
The client wanted each folder’s images to be numbered 001.jpg to nnn.jpg for some further process.

import os
import imghdr

def renamefiles(path):
rootstructure=os.path.abspath(path)
n = 0
for root, dirs, files in os.walk(rootstructure):
for f in files:
if os.getcwd() != root:
n = 0 # Reset the counter
os.chdir(root)

type = imghdr.what(f)
if type == 'jpeg':
n +=1
os.rename(f, str(n).zfill(3) + ".jpg")

# Specify the full path to the directory here.
renamefiles("/Users/myuser/Desktop/TheImageFolder")