|Credit: see below|
Amatzia Avni suggests, tentatively, that the person on the far left in the front row is Reuven Mauer (ph. spelling of ראובן מאוער), 'the mythological secretary of the Lasker chess club in Tel Aviv'.
If these two identifications are correct, they would be the two "extra" persons, apart from the 13 players, in the photograph.
ETA 31/4/2017: Yochanan Afek notes that it is not likely it is Mauer, due to the date of the photograph, taken when Mauer was much younger than the person in the photograph.