CSS Opacity

I think it is very inconvenient that when you set opacity on an element
you cannot make descendants opaque.

Consider this example (perhaps with some scripting involved):

You want to show a photo in the middle of the page and make the rest of
the page semi-transparent.

body { opacity: .5; }

Will make the photo semi-transparent as well.

#photo { opacity: 1; }

Will not fix this.

People are forced to use workarounds like this:
http://reisio.com/temp/punkid/

Which requires extra elements and not always possible.

Forgive me if I am failing to see the implementation limitations, but in
my personal opinion opacity override is something that would be quite
useful.