Cheetahs are not part of the Big Five, but they are beautiful animals and great photographic subjects. If you specifically want to see and photograph cheetah during your African safari, you should carefully plan where to go to be sure to see them.
Open savanna and bushveld are the preferred areas for cheetah. They provide the best conditions for their hunt as high-speed predators. Prime wildlife destinations like the Masai Mara in Kenya, the Serengeti in Tanzania and other areas with open plains are ideal to watch and photograph these amazing animals. Otherwise excellent areas like the Sabi Sand in Kruger, South Africa, offer only in their northern part the possibility to see cheetahs. Plan carefully where to stay in these areas to not be disappointed. Often camp and lodge websites provide information on the wildlife that can be seen. Some have a blog on the wildlife sightings, which give a good idea what to expect. Also ask specialized tour operators for advice.
An excellent option to see and photograph cheetah in South Africa is Phinda Private Game Reserve. It might feel a bit out of the way as it is not in Kruger, but it offers great sightings.