You may feel as though your privacy is being violated if your neighbor installs a security camera which—inadvertently or otherwise—captures activity in your yard. Yet there are no laws in Maine which prevent a person from installing cameras pointing outwards from their own property.
The law does not treat your backyard or the outside of your home as spaces where you have the reasonable expectation of privacy. Your neighbor is allowed to visually record you in these spaces for the same reason that Google can take satellite images of your land.
If you find yourself in this situation and are uncomfortable, you may try speaking with your neighbor or installing something on your own property to block the camera’s view. These solutions are of course more likely to be effective if your neighbor is well intentioned and your property simply appears in the background of their recording.