1. A method, comprising steps of: receiving a first image with a first focal length and a first field of view; receiving a second image with a second focal length longer than said first focal length and a second field of view substantially identical to said first field of view; defining a plurality of element sets, each said element set comprising a first element in said first image and a substantially corresponding second element in said second image; comparing said first and second elements in said element sets, with regard to a relative focus thereof; assigning as background any of said element sets wherein said second element thereof is more in-focus than or substantially equally in-focus as said first element therein; and excluding said element sets assigned as background from further analysis.