I'll vote with Hypersmurf on this one. It's the way our group has played the interplay between magic missile and mirror image since 3e came out (and contrary to the way we played it in 2e). You can fire your multiple magic missiles, one at each image, in order to ensure you get at least one hit on the real wizard, but the other missiles are wasted and don't take down the images. If you want to take down the images, get your trusty archer with rapid shot to pick 'em off (remember, the images' AC is often only 10 or a mite above). An alternative for wizards is to use one of the lesser orb spells from Tome and Blood. Since this spell requires an attack roll, I have ruled that it takes down images - and a wizard gets as many lesser orbs as he does magic missiles.
Cheers, Al'Kelhar.
Cheers, Al'Kelhar.