1. A method, comprising: receiving a first image with a first focal length and a first field of view; receiving a second image with a second focal length and a second field of view, wherein the second focal length is longer than the first focal length, and wherein the second field of view is similar to the first field of view; defining a set of elements comprising a first element in the first image and a second element in the second image, wherein the first element substantially corresponds to the second element; determining a first rate of change of an image property of the first element, the first rate of change is indicative of a first focus level of the first element; determining a second rate of change of the image property of the second element, the second rate of change is indicative of a second focus level of the second element; and assigning the set of elements as background elements when the second focus level is greater than or equal to the first focus level.