When a cop takes a picture of your house it can mean they are investigating something such as something illegal that someone reported or they could be taking a picture of the house as they believe someone they want is living there.
Cops can take a picture of your house but to enter property they need a warrant and they cannot go past locked gates or fences without a warrant or consent.
It could also be someone pretending to be a cop and they are casing your house to rob it later on.
I would contact the local police stations non emergency number and confirm that a cop was actually there taking pictures.
You can also advise them not to do so anymore or advise them to stay away from your property or you could sue them.
If you're doing nothing wrong and the police are just harassing you then you can put in a complaint and even sue the police.