It won't change as avatars are located on another server and are set to change roughly every three hours.
And as far as people accusing you of using others' avatars? If more than one person has said it, there might be some merit to their statements. At least on one occasion, the image selected by you even had the specific, unique MacRumors' attachment ID as the 'tar created from scratch by a well-established MR member (who still uses that 'tar today).
I can't speak for other incidents, but the one I mentioned has been documented.