Kenya, Tanganyika and Uganda were once British colonies. The stamps in those days generally bore the portrait of King George with Lake Naivasha in the background. The stamps in left column above were printed in late 1930s.
The stamps bearing the portrait of Queen Elizabeth II are of the period after her coronation, especially 1959. These stamps continued till the three courtiers became independent. Tanganyika on independence split in to today's Rwanda, Burundi, and Tanzania. All three countries became independent states in the early 60s.
Lake Naivasha (Wikipedia)