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[Hypersmurf]

There are no mention of an attack roll being necessary in the Mirror Image description, so I see no need to turn to the FAQ to let Magic Missiles work.

I'm at work, so I don't have access to my PHB. SRD says :

"Enemies attempting to attack the character or cast spells at the character must select from among indistinguishable targets. Generally, roll randomly to see whether the selected target is real or a figment. Any successful attack roll against a figment destroys it. A figment’s AC is 10 + size modifier + Dexterity modifier. Figments seem to react normally to area spells."

Even if the PHB leaves out the word "roll", we still need to go to the FAQ... because Magic Missile targets creatures, and Mirror Images are not creatures. It's not until you admit the FAQ ruling that the spell can have any effect on a figment.

-Hyp.