Question

Here an example http://jsfiddle.net/6GdW6/

$(".thumbnail").live("click", function() {
    $(".fullimage").hide();
    var i = $("<img />").attr("src", this.href).load(function() {
        $(".fullimage").attr("src", i.attr("src")).addClass("selected");
        $(".fullimage").fadeIn();
    });
    return false;
});

1. How to show first image by default if no click?
2. How to add selected class only on active link?

I want to keep current html format.

Answer 1

$(".thumbnail").on("click", function() {
    var selector = '.fullimage[src="' + $(this).attr('href') + '"]';

    $(".fullimage").hide();

    $(selector).fadeIn();
    return false;
});​

http://jsfiddle.net/6GdW6/2/