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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _changeGroupImage(self, image_id, thread_id=None):
 """ Changes a thread image from an image id :param image_id: ID of uploaded image :param thread_id: User/Group ID to change image. See :ref:`intro_threads` :raises: FBchatException if request failed """

        thread_id, thread_type = self._getThread(thread_id, None)

        data = {"thread_image_id": image_id, "thread_id": thread_id}

        j = self._post(self.req_url.THREAD_IMAGE, data, fix_request=True, as_json=True)
        return image_id