An apparatus and a computer-implemented method are provided for determining a location in a target image (T) of a site on a surface of a physical object using two or more reference images (I1, I2) of said physical object that have been obtained with a reference imaging device. Each of said two or more reference images includes said site on the surface of the physical object and was obtained with the reference imaging device having a different position and/or orientation relative to said physical object. The target image is obtained by a target imaging device and includes the site on the surface of the physical object. For each reference image, a set of feature mappings from the reference image to the target image is used to determine the epipolar geometry between the reference image and the target image, and a projection of the site from the reference image onto the target image is calculated from said epipolar geometry. The location in the target image of the site on the surface of the physical object is determined from the calculated epipolar projections for the two or more reference images.