For the time being
(as long as not every browser supports css-3 and/or semi-transparent png's):

SEMI-TRANSPARENT DROPSHADOW
FOR MOZILLA/FIREFOX AND INTERNET EXPLORER,
without the IE png-hack,
just simple css.

Browsers without css-3 opacity-support just show a non-transparent shadow,
details see bottom of the page.

No png's, but 2 transparent gif's,
see source code!

Use smaller window and window-grip for hovering the image all over the page.


 

Detail with transparency:   Detail without transparency:
 
 The shadow-gif's have (100%) transparent corners: