If I were the tenant, I would totally object to this. No matter how innocent your motives, even very nice people don't want to think they are being monitored.
Let's say the back yard is enclosed. The owner might want to monitor it. The tenant might want to sunbathe. Even if in a bathing suit, who'd want to stretch out in front of a stranger?
I can think of a couple of ways this might be doable. One would be to limit the camera(s) to driveway and front door views. The other would be to offer a $200 per month discount on the rent. Think about it as money versus privacy.
Has any of us known their landlord well enough that they would want him watching them?
A good answer is easier with a clear question giving the make and model of everything. "The biggest problem in communication is the illusion that it has taken place." -- G. “Bernie” Shaw