def markdown_attribution(app_name: str, author: str, profile_url: str) -> str:
    """
    :param app_name: This app's name.
    :param author: Author name.
    :param profile_url: The author's name.
    :return: Markdown string attributing the user at Unsplash for a photo.
    """
    unsplash = "https://unsplash.com/"
    params = f"?utm_source={app_name}&utm_medium=referral"
    return f"Photo by [{author}]({profile_url}{params}) @ [Unsplash]({unsplash}{params})"