I've tried various conventions to move from one picture to another, haven't had any success yet. After I view a thumbnail I use the "back" key for the browser. It would be nice to be able to tab or click from picture to picture.
I won't say most, but many boards don't allow much in the way of posting pictures, too much abuse and moderation. Sort of have to have it for us crafty types, but doesn't go so well with the socially maladjusted type of forums, so I don't know how high on the priority list something like that would be for the programmers.