change the markup to
<div id="containerA">
<img id="imageA" src="http://www.w3schools.com/images/tryitimg.gif" alt="imageA">
</div>
<div id="containerB">
<img id="imageB" src="http://www.w3schools.com/images/w3logotest2.png" alt="imageB">
</div>
<div id="containerC"></div>
and do
$(function(){
$("#imageA").on('click', function() {
var container = $("#imageB").closest("#containerC").length ? $("#containerA") : $("#containerC");
$("#imageB").appendTo(container);
});
$("#imageB").on('click', function() {
var container = $("#imageA").closest("#containerC").length ? $("#containerB") : $("#containerC");
$("#imageA").appendTo(container);
});
});