You can use the after parameter like
var lastId;
function load(params) {
params = params || {};
$.getJSON("http://www.reddit.com/r/pics/.json?jsonp=?", params, function (data) {
var children = data.data.children;
$.each(children, function (i, item) {
$("<img/>").attr("src", item.data.url).appendTo("#images");
});
if (children && children.length > 0) {
lastId = children[children.length - 1].data.id;
} else {
lastId = undefined;
}
});
}
load();
$('.after').click(function () {
if (lastId) {
load({
after: 't3_' + lastId
});
}
})
Demo: Fiddle
See this answer