Shadow background on pop up css image(how to?)

Hi i was wondering if someone would know how to change the alpha or the brightness of the page. An example of this is when someone click on a picture, the image apears on the screen bigger and the background is like less to be seen so you can have a better focus on the image.

This can be seen at this web page
http://www.worldofwarcraft.com/downloads/ssotd/#latest


I appreciate any answer to help me

good day!!

 

I recommend Lightbox http://www.huddletogether.com/projects/lightbox2/

 

So i guess its more complicated than a simple command to use .. It requires a whole set of libraries

thanks for this