change_image_file_name.py

import os
import datetime
from time import sleep

for file in os.listdir(os.getcwd()):
    if file.endswith('.jpg'):
        os.rename(file, "img_"+datetime.datetime.now().strftime("%Y%m%d-%H%M%S%f")+'.jpg')
        sleep(0.05)        

this script is able to change image file names in current directory
for unique names I used datetime
for avoid race conditions I used sleep function in time library