If I showed you this picture, and asked which one is Mick, what would you say?
Does the right/left orientation point come from the viewer’s perspective, or the people who are in the photo?
Second from the left. I always thought it was the viewer’s perspective.
Not a rule or anything, but from the picture’s perspective I would say Second from THEIR right.
Second from the left.
Viewer’s perspective would be standard
Huh?
There is only one answer: 2nd from the left.
Imagine that it was a picture of 5 trees, not people—and you asked which one is the Maple? (assume that the Maple is where Mick is standing)
You would count from your left,not from “picture’s perspective”.
Well,I would.
So that settles it, 'mkay? 
Alas, I don’t have any examples handy that I can check, but if I remember correctly the convention has always been that, when there’s a caption with a picture that identifies who’s in the picture, “left” and “right” always refer to the left and right side of the picture itself (from the viewer’s perspective).
Well, I agree, but the reason I started this is because someone argued vehemently that I was wrong, and made it quite clear that the orientation was from the people in the photo. I wondered if anyone else had this bizarre and totally wrong viewpoint as well.
I’d say second from the left, whether it’s a photo, or if they’re standing in front of me. It’s my left as I’m looking at them.
From the left. Saying “Second from Their Right” is just forcing the person looking at the picture to do the “Math” of converting it back to their own perspective whereas starting from their own perspective saves the trouble.
What color hat were they wearing?
It would be interesting to raise this question in Israel or an Arabic country because my guess is that it is related to our left to right reading.
I didn’t notice a hat, but she was wearing a blue striped dress and saying “Yanni” over and over. I think it was Yanni. If you see someone in a white striped dress saying Laurel, that’s probably her.
If you don’t specify differently, then describing a picture is from the viewer’s perspective.
If you do specify differently, please only do so for a very good reason, and in a way that a stupid person could understand. 
I’m not saying there’s never a reason, just that it should be a good one.
I have seen captions that will say something like “Bob X stands at Susie’s right” or At Susie’s right hand is Bob X." But overall it’s very confusing to do it that way. Left to right as displayed to the reader is always best.
I agree, unless for example Susie’s actual literal right hand was an important part of a story being told.
Second from the left, second from stage right.
“He’s the one with the lips.”
This is what I was going to post. The default is from the perspective of the viewer. If we mean something different, we qualify it specifically.
Depends. If they’re below the equator, then it would be second right.