Photo postcard by Pereira de Lord 1904 Zanzibar.
Chained convicts unloading a ship in Zanzibar (forced labour) 1904 or earlier.
Postcard showing forced labour by convicts in Zanzibar
Chained convicts at work on a boat. This postcard with the title "convicts at work" was issued in 1904 by Pereira de Lord photo artist in Zanzibar. See Ref 2. The photo was probably taken earlier than in 1904. Again the same chains and and collars used on these workers unloading a ship were previously ere previously used for slaves.
Below you find a You-tube film regarding the slavery history of Zanzibar: