The mirror image spell description says
Each time a creature targets you with an attack during the spell's duration, roll a d20 to determine whether the attack instead targets one of your duplicates.
It does not prohibit targeting the illusory duplicate themselves, especially for a non-hostile effect.
Two examples from features with a similar effect are:
The Goblin Boss (MM, p. 166) has the Redirect Attack reaction:
When a creature the goblin can see targets it with an attack, the goblin chooses another goblin within 5 feet of it. The two goblins swap places, and the chosen goblin becomes the target instead.
The Way of the Drunken Master monk's 6th-level Tipsy Sway feature also grants a benefit named Redirect Attack (XGtE, p. 34):
When a creature misses you with a melee attack roll, you can spend 1 ki point as a reaction to cause that attack to hit one creature of your choice, other than the attacker, that you can see within 5 feet of you.
Note that those are just examples. The point of the question is whether the duplicates can be targeted by such attacks or effects, either knowingly or unknowingly it's a duplicate.
Also note that most non-attack effects simply bypass mirror image by directly affecting the mirror image user. However, for other effects, this question asks about the more fundamental principle: whether the duplicates are actually targetable or not.
A point of consideration might be whether an effect that specifies a creature as its target is unable to target mirror image's duplicate – or whether any effect is simply unable to target the duplicate, and could only target the original target.
Best Answer
The duplicates aren't creatures
Per the mirror image spell description:
Nothing in the spell description says the duplicates are creatures - they're just illusory copies of you.
...But attacks can always be redirected to them regardless
The description continues (emphasis mine):
Anytime you're targeted by an attack while mirror image is active on you, the spell can redirect the attack to one of your duplicates. The spell makes no exceptions regarding whether the attack can only target creatures.
As the intro to the PHB/basic rules states:
It's because "specific beats general" that any attack that targets you, even if it normally can only target a creature, can be redirected to a duplicate as well.
The duplicates can't be intentionally targeted, either
The illusory duplicates can't be intentionally targeted separately from you. As the first quoted pair of sentences state, it's impossible to track which image is real because they move with you and mimic your actions. Thus, anything that would attempt to target your duplicate would necessarily have to be trying to target you - which of the "duplicates" actually turns out to be you is determined randomly by rolling a d20.
Anything that's not an attack doesn't interact with the duplicates
A later part of the spell description says (emphasis mine):
As the spell itself states, the illusory duplicates have no mechanical interaction with things that aren't attacks - whether it's a spell requiring a saving throw, a non-attack monster ability, a class feature, or something else. Unless it's an attack, it doesn't interact with the spell at all.
(Note: grapples/shoves are "special melee attacks", so they can be redirected to the duplicates - but since they don't have attack rolls, they can't "hit" the duplicate and simply fail if redirected to a duplicate.)