myapp/cli/params.py

from typing import Any

import click
from PIL import Image


class ImageParamType(click.ParamType):
    name = "image"

    def convert(
        self, value: Any, param: click.Parameter | None, ctx: click.Context | None
    ) -> Any:
        if value is None or isinstance(value, Image.Image):
            return value

        try:
            return Image.open(value)
        except OSError as e:
            self.fail(str(e))