I've made this little popup very simple, check it out!

translucent popup example

The translucent class makes it all possible, to add this to your pages, you'll need to assign IDs to the images you want the effect on, then look for this line:

pU.p("image1","inTensa/g1.jpg");

The first argument (image1) is the image ID for the thunmbnail
The second argument (inTensa/g1.jpg) is the full size popup URL

Add one line per image you want the effect on. Happy codeing!