Sugar-cane is grown on Zanzibar. On the photo we see sugar-cane being processed and cooked to to produce sugar-cane-juice. The popular juice is still being drunk in Zanzibar and Oman today. The Ostrich looking on in the background and hoping to get some leftovers.
Production of sugar-cane juice Zanzibar
Detail of the above photo with the Ostrich looking on
All the workers wear the same cloths and a metal badge with numbers on a string around their neck. It is very likely that these badges are the proof that the person is a free man! Ref 1 confirms this practice in East Africa. Ref 2 and 3 show a photo with slaves freed up by Nicolas Tobback in Kisingani that also have a badge around their necks.
If anyone knows more about these metal badges in Zanzibar let us know!!!
Military campaigns produced large number of captives who were then declared liberated as state soldiers and missionary orphans. Catholic missionaries were actively involved in ransoming slaves and turning them into converts and workers. So probably the people above are freed slaves involved in a work training programme by missionaries, which may also explain why they are clothed identical.