Tony Vargas
Legend
Depended on your DM. Also on the edition - IIRC, Magic Missile wasn't always an auto-hit.But in the grand old days of previous editions, wasn't magic missile the traditional counter to mirror image because you could target all the images simultaneously and guarantee popping them all?
Of course, 5e Magic Missile uses the word 'hit.' 5e isn't written in precise jargon, it begs to be interpreted by the DM. While the 'RaW' interpretation might be of token interest, it's hardly the most important thing to consider when making a ruling. What works best for your game being way out in front.Also, the word 'hit' implies an attack roll in 5E.
For instance, I see nothing wrong with either the ruling that you can target 1 missile each of a 2nd-level-slot MM per apparent target presented by a Mirror-Imaged caster, thus hitting the caster once and dispelling his images, nor with the ruling that you can just cast MM at the caster of the Mirror Image and have them all strike him (and appearing to injure all the apparent targets involved). Even allowing it to work one way or the other under different circumstances wouldn't be too crazy. But, I'd see issues with ruling that the spell could 'miss' without dispelling images (because they're not creatures) or both hit the caster and dispel his images with the same missile (because they're some blurry overlapping cloud).