Q. Which is the correct form when informally captioning a photo: “Lenny and me at the store” or “Lenny and I at the store”? I always use the former, reasoning that you would not caption a photo “I at the store,” but many people have “corrected” me.
A. “Lenny and me at the store” is perfectly correct; the caption is an elliptical sentence that might be expanded as follows: “This is a picture of Lenny and me at the store,” in which “Lenny” and “me” are both objects of the preposition “of.” As you have discovered, however, many people assume that “and me” must always be wrong, even where an object (“me”) rather than a subject (“I”) would normally be expected. This avoidance of “and me” in favor of “and I”—for the sake of politeness perhaps, or to avoid the appearance of making a mistake—isn’t the end of the world, but you should stick up for what’s right and insist on “Lenny and me.” After all, writers and editors have some say when it comes to how words are arranged on the page, informally or otherwise. (But don’t correct another person’s speech, and don’t be that person on social media. It’s not nice.)