How can I remove a black/gray border from a black & white image without compromising the inside details? Code or workflow would be helpful

Question

How can I remove a black/gray border from a black-and-white image without compromising the inside details? Code or workflow would be helpful.

Expected result: I want to remove the black or gray border line from the image. Removing null values does not help because the borderline has different values and is not entirely black. I want to remove the continuous black/gray border line without compromising the image details.

Please look at the attached sample image. Aerial Image