I love the photo, and the model is one of my favorites in your...?... "Collection". It’s a Martial Arts expression, or salute. There should be a progression from the physical to the spiritual in pure “Martial Arts.” An evolving from being purely warrior to being the warrior/scholar, which is shown in the hand salute in this photo. The open hand is the priest or scholar, and the closed fist is the warrior, the two exist together as Ying and Yang do completing a whole. Sadly, over the years, this progression has been lost. Martial Arts no longer has the original accompanying spiritual philosophy! What passes for philosophy in most martial arts schools would shock the ancients with its shallowness.
well a friend of mine does all kinds of martial arts from ( please don't kill me for wrong spelling but i have no clue how to spell most of them ) Jiu Jitsu, Thia Boxing, Karate, Kung Fu and a few more, and he's doing his Doctorate in engineering right now. I guess that passes as a modern martial artist.
Many many arts use this universal pose, so there is really no wrong or right answer. In my particular system, Kenpo, we use it as meditation salutation just before and after bowing in on the mat in the dojo. It's also in our formal salutation. You can read the Kenpo Salutation and see the bow performed by the late Ed Parker here, [link]
Our 'Little Dragons' also call this pose the "Jewel in the Pocket" when the open hand covers the fist. It's to remind them that they should keep their abilities to themselves and not let the 'outside world' know about it unless they have to. (no showing off at school idea )