Most irritating, and it creates some risk. Do you have any idea why the person did this? Would they be amenable to taking the pictures down? The next stage of analsys is if they violated the law in taking the pictures. For example, it is one thing to take a picture at the public playground or the mall, another to sneak around, perhaps onto your land, and take a picture of your fenced yard. That would be an invasion of privacy. At present, the is little else to "hold them accountable for" since you have suffered no actual damage. Consider this step by step, and consult with an attorney where you can safely present all of the facts.
We do not have a client/attorney relationship until you make an appointment, we discuss your case face to face, I accept a retainer, and we explictly agree to enter into representation.