A first depth map is generated in response to a first stereoscopic image from a camera. The first depth map includes first pixels having valid depths and second pixels having invalid depths. A second depth map is generated in response to a second stereoscopic image from the camera. The second depth map includes third pixels having valid depths and fourth pixels having invalid depths. A first segmentation mask is generated in response to the first pixels and the third pixels. A second segmentation mask is generated in response to the second pixels and the fourth pixels. In response to the first and second segmentation masks, a determination is made of whether the second stereoscopic image includes a change in comparison to the first stereoscopic image.