This is the 10588th most frequent Russian word.
внешний
External; outer.
Here, "внешний" is used to describe an attribute (appearance) specifically related to the outside or external of the building.
Внешний вид здания впечатлил всех.
The exterior appearance of the building impressed everyone.
In this sentence, "внешняя" (forms of "внешний") characterizes the camera as external, suggesting its placement outside.
Установите внешнюю камеру для видеонаблюдения.
Install an external camera for video surveillance.
Here, "внешний" denotes 'external opinions,' referring to perspectives or ideas coming from others or outside one's inner circle.