One of the tasks of the British, and other European, troops on Crete was to disarm the Cretans. The Muslim population were mostly based in the larger towns on the north coast of the island, towns occupied by European forces, and their disarmament was straighforward. In the Christian controlled centre and south of the island European officers went out into the villages and working through the local chietens and political leaders, arranged the ‘voluntary’ disarmament of the local population.
Judging by the flags on the left of the picture, this photograph probably shows a Russian detachment receiving weapons from Cretan Christians. British troops carried out similar exercises in their secteur of control, Candia
The flag on the right hand side of the photograph is almost, but not quite, the flag of the Cretan Autonomous State. The one displayed here, with a cross in the upper left quadrant, was the version that was rejected by the European Powers. The objection to it was that it had two (Christian) crosses on it which was deemed to be politically insensitive since the Cretan Auonomous State had been created upon the expulsion of the Ottoman (Muslim) authorities by the Powers. The official flag had a star in the top left quadrant, representing the minority, Muslim, population of the island.
More information on the significance of Cretan flags can be found here.