Check it out live : http://sathyaprasad.appspot.com/swipe.html
I did go through the challenges one at a time and was able to get the tool to do all the things. Well you will not believe how simple the solution was. The thinking was all the images from the layers are on the map, just clip it. CSS does support “clip” and this tool makes full use of that. Check out the code for more details.
Hope you like this tool and use it in your applications.