Renames DSC_x.JPG to DSC_x+999.JPG to reorder pictures when a new folder has been created after DSC_0999.JPG and the pictures in the new folder start from DSC_0001.JPG again.

recounter.py

#!/usr/bin/env python3
import os
import sys
from shutil import copy2
from pathlib import Path

if len(sys.argv) != 2:
    raise Exception("Invalid number of arguments. One directory path must be provided.")

p = Path(sys.argv[1])

if not p.exists():
    raise Exception("Specified path does not exist.")

pictures = p.glob("*.JPG")

if pictures:
    od = p / "recounted/"
    if not od.exists():
        os.mkdir(str(od))

for picture in pictures:
    name = picture.name
    number = int(name[4:8])
    o = p / "recounted/DSC_{0}.JPG".format(number + 999)
    copy2(str(picture), str(o))