If you are trying to do a standard image linking between two images that have different dimensions and pixel sizes, it won't work because they are linked by samples/lines and when you move from pixel to pixel, it will not be the same location. But you can do a Geographic link. Does this work? To do a standard link with a dynamic overlay, you will need to resample one of the images to the other. It is probably best to also make sure they are the same number of samples and lines but it isn't necessary. If the pixels are coincident with each other, you can set the x/y start in one image to match the x/y location of the other but it can be a little tricky to get them to match up. It might be easiest to do a Layer Stack on the images.