[TygerTyger]

A note on the code:

Due to Internet Explorer and older versions of Mozilla using proprietary opacity code (Yes, Mozilla fanboys must hold their hands up too this time) this will break your CSS W3C compliance. It won't make any difference to the functioning of your page, you just won't be able to say it's compliant.

This is not necessarily the best version of image opacity code, but it is the most compatible. It will work in all current major browsers except Opera (lagging behind somewhat, but when they catch up you should be ready) and should degrade gracefully to around NN4 and IE4 (but don't hold me to it.) although it does mean you can only use it on hyperlinked images. There are other ways of doing this, but you'll lose the effect in some browsers, most notably IE which has the most trouble.

If anyone comes up with more widely compatible CSS I'll update to include it.