in the case of the unknown guest, as they won't be doing a signing after then it is unlikely they will have time for photos. I suspect the same would apply to the all guests. If everyone wanted to do that (quite likely) you are looking at a lot of time involved. No. If you want a photo taken with a guest you'll either need to check if they're doing photos at their table when you get an autograph or in case they don't do that you'll need to get a photo session ticket.
In any case you'll already all be seated when the guests arrive, so even in theory there's no chance to do that.