The "box" 4-tuple parameter of the PIL.ImageTk.PhotoImage.paste method is intended to allow a PIL Image to be pasted onto a Tkinter compatible PhotoImage within the specified box coordinates, but "box" appears to be dysfunctional, and I can't see anything in the source code of the method to implement its function. Smaller images pasted to larger images appear top-left and ignore any "box" value.

The documentation detailing the "box" parameter is here:
https://pillow.readthedocs.io/en/stable/reference/ImageTk.html#PIL.ImageTk.PhotoImage.paste

The source code of the paste method includes "box" as a parameter and has a docstring for it:
https://github.com/python-pillow/Pillow/blob/main/src/PIL/ImageTk.py#L178

Test code. A smaller blue box pasted into a larger yellow box always appears top-left and ignores the paste coordinates:

import tkinter as tk
from PIL import Image, ImageTk
root = tk.Tk()
pil_img1 = Image.new("RGB",(400, 200), "yellow")
tk_img1 = ImageTk.PhotoImage(pil_img1)
tk.Label(root, image=tk_img1).pack()
pil_img2 = Image.new("RGB",(200, 100), "blue")
tk_img1.paste(pil_img2, box=(100, 50, 200, 150))
root.mainloop()

Tested with Windows 10, Python 3.10.4, Pillow 9.0.1
and with Ubuntu 21.10, Python 3.9.7, Pillow 8.1.2