The image-level matching algorithm at work (top: UGC 7360, bottom: NGC 0547). In step 1 and 2 we determine the size of the frame and draw contours. In step 3 we find the pixels above the value of the outer contour (labeled with red plusses) and in step 4 we link these pixels to the optical center of the galaxy (green squares). In step 5, we find the pixels that are connected to the group obtained in the previous step (shown by green circles), these define the radio emission matched to this galaxy. Finally we measure the geometrical center (white cross) and the flux-weighted center (cyan circled cross). For the latter, we use only the pixels that contain 80% of the total flux of the group (labeled with blue squares).