The search words I used were "West African people [and] albumen or silver gelatin." You could try other combinations of these words with country names instead of W. African or daguerreotype, etc.

https://www.google.com/search?safe=active&tbm=isch&sa=1&ei=3I0TWpPlDOKa_QaPnI2AAw&q=vintage+west+african+portraits+albumen&oq=vintage+west+african+portraits+albumen&gs_l=psy-ab.3...40538.57422.0.59962.20.15.0.0.0.0.4920.11686.0j9j2j9-2.13.0....0...1c.1.64.psy-ab..7.2.331...0i7i30k1j0i8i7i30k1.0.bL1pJiFZmFc

https://www.google.com/search?safe=active&tbm=isch&sa=1&ei=Go4TWvfII5Kpggfy5ZLAAw&q=vintage+west+african+people+albumen&oq=vintage+west+african+people+albumen&gs_l=psy-ab.12...28937.30344.0.33034.6.6.0.0.0.0.185.755.0j5.5.0....0...1c.1.64.psy-ab..1.0.0....0.9lb23W4Gqi0

https://www.google.com/search?safe=active&tbm=isch&q=vintage+west+african+people+silver+gelatin&spell=1&sa=X&ved=0ahUKEwir0967zs7XAhUjneAKHXkWCzgQvwUIOygA&biw=1184&bih=558&dpr=1