Complex roll-over?

Complex roll-over?

Ok so here's a picture
http://i14.photobucket.com/albums/a309/ ... egular.png

There are 4 squares in that image. I want to be able to mouseover each of them, and accurately do so (even the ones behind the others).

Once I mouseover these images, I want an effect (let's say drop shadow) like so

http://i14.photobucket.com/albums/a309/ ... /green.png

or


http://i14.photobucket.com/albums/a309/ ... yz/red.png

Any ideas as to how the best way to achieve this would be? I looked around and the only ways I could find to do it were unfavorable solutions.