Ok, just for fun I had to share this. Check out the picture at the bottom of this web page:
http://www.dataflo.net/~mpurintun/blues_notes.htm

Music, the universal language.

Thanks. Great photo!

I'm wondering about the instrument front left. Looks like it might be a no-hole flute, but I have doubts about the embouchure.

But why do I have the sens that the person holding the concertina doesn't actually know how to play the thing?

Look at the fingers. Even if you or I were posing for a picture and not playing, would our fingers likely take on such a clueless position?

I wonder if a harmonica player would say something similar about the way that instrument is being held. Ans shouldn't the resonator on the bow be aimed at the audience, rather than toward the "musician's" chest?

No, the berimbau is played with the gourd resonator pointed towards the chest. The tone is modulated by pressing the opening into the body and moving it away again, giving a "wah-wah" sort of sound.

A quick search found some samples:
http://www.capoeirista.com/music_rhythms.html

The unusual poses might have something to do with the way they had to stay still for so long, required with early photography.

David.when I pick up my heavy-as-hell 44key Jeffries,it assumes this exact position ! Hence the knee support or whatever. Robin

This photo, with many others, can be found as part of the extensive liner notes for the "Squash Box" CD issued by Silex/Memoire in 1993.

Oh! By the way, these concertina players can play. They just don't play 'the thing' the same way you/we are used to hearing it played.

As for the harmonica player, he (she?) was probably instructed to hold the instrument so that it could be seen. To really play effectively, one must fold the harp deep into ones hands.
Wonder what the repertoir was like?

Add to that in 1900 film, lenses, etc. were still very slow. They didn't do snap shots but rather posed. These souls very likely had be sitting for this picture and perhaps previous poses for many minutes and may have been very weary of it all. It is way too bad that we can't hear them.