A discussion on Twitter this morning reminded me that there are, indeed, still folks out there who insist on “It is I” and similar constructions with pronouns.
English is not algebra. What’s on one side does not have to equal what’s on the other side. That is, when it comes to pronouns, what’s on one side of the verb “is” does not have to be the same case (nominative) as what’s on the other side.
In other words, “It is I” is stuffy at best. Very formal registers may well insist on it, but for other writing? Let out your corset, honey. We can say “It is me” and nothing will happen. No cataclysm will result. (We can really let loose and say “It’s me” if we’re of a mind to use a contraction.)
Technically, that “me” or “I” in “It is [me or I]” is a predicate nominative. If you’re being absolutely “correct,” and in the most formal registers as I just said, you’ll indeed want to use “I” in that position, matching the case (subjective) to the purpose (standing in for the subject). However, writing captions for photos doesn’t require high register. You’re labeling folks in a Polaroid, maybe, and you want to make sure they will know who’s who. “Roger, me, and Marian at the lake” is perfectly acceptable here. “Roger, I, and Marian at the lake” sounds like Countess Crawley wielded a dip pen over the back of the photograph.
But don’t take my word for it. Check out Woe Is I by Patricia O’Conner, or visit Mignon Fogarty’s “Quick and Dirty Tips” for this tidbit.