Use of "being" in literary prose [closed]

I feel silly asking this but I can't find the answer anywhere (including CMOS, dictionaries, etc.). I am a professional editor and am struggling with an author who uses "being" in the following way: He has a sleeve of tattoos on his left arm—the most prominent being a picture of Bettie Page. I mostly see this usage in romances or with British authors. What is "being" and why should I not change it to "is" to retain her phrasing. Thank you!!!

The difference is actually rather simple. If you use is, then the second part is a sentence in its own right. You are writing two sentences, and I would actually expect a full stop to separate them.

If you use being, the second part of the sentence is an absolute clause (thank you @ColinFine) that brings further information about the word "tattoos". As the wikipedia link given notes, it "is not particularly common in modern English and is generally more often seen in writing than in speech".

For what it's worth I would definitely write being in this case.