Technically, we aren't suppose to call the same mark again. But if it happens like this,(it was done in July of 2012), I think whoever got the mark the first time can just repost their picture and claim the prize for the day and call the next mark. Kind of a bonus score.
Or anyone else is free to try for it also.
Not a big fan of rules, so if it makes the game move along faster, it's all good.
This game has been going on for almost 2 years and it is kind of difficult to find out what hasn't been called yet.