1. A method of detecting potential changed objects in a first image and a second image, where the first and second images at least partially overlap, the method including: obtaining data describing a first image and data describing a second image; detecting a first set of objects in the first image data; detecting a second set of objects in the second image data; calculating a common coordinate system for the first set of objects and the second set of objects; converting locations of the objects in the first set and/or the second set into the common coordinate system; targeting of said objects in the first set and the second set based on positions of the objects in the sets; targeting of said objects in the first set and the second set that are located outside an area of overlap of the first image and the second image; and outputting data indicating zero or more of said objects in the first set and the second set as potential changed objects.