Wait wait wait… what? Oh geez, that’s not what I had in mind at all.
I was thinking more along the lines of the Catholic school-girl tight sweater “show me those gazongas” line. Gah, I could explain it better but I found a link that does the job for me:
**Auto, ** your reputation has gotten way out of hand on here. 
I would hazard a guess that only the thin and/or limber can actually touch their elbows together in this manner. Being neither, I of course cannot do it.
Pfft. You can do that without touching your elbows together; you just need to get sort of close for that.
Certainly the picture is taken from the wrong angle. 
I can barely touch my elbows in the front. My pecs are too tight.
I can do it easily. I can also put my hands palms together behind my back, fingers pointing up (think a classical praying pose, but behind your back rather than in front), then raise them up (still together, still fingers up) to between my shoulder blades. It’s a question of internal rotation of the shoulders, not really of flexibility, exactly. FWIW, I have really lousy internal rotation of my hips - I can’t do forward-facing splits, or a good butterfly pose (where you put the soles of your feet together while sitting on the floor, draw them towards your body, then try to get your knees to the floor), so apparently the two things don’t necessarily go together.
I first noticed the elbows-together thing when I was a kid, reading an article about a civil war somewhere in Africa (Uganda, maybe) that talked about how one side would torture people by binding their elbows together so that they couldn’t breathe. I remember wondering why one would lead to the other, since it didn’t give me any problem.