There is no term for photos that don't involve people.  Photos are categorized based on what they are of, not what they are not of.  A photo is not of an infinite number of things.  

If I take a photo of my wife indoors, it is not of outside, it is not of cats, it is not of nighttime, it is not of waterfalls, it is not of ants, it is not of the future, it is not of a TV, it is not of stars...

Having a term for what photos are not of simply doesn't make sense.