1. A method for registering first and second digital images, said method comprising the steps of: transforming said second digital image to be more like said first digital image using a modification function, to provide a modified second digital image; determining a set of first features of each of said first and modified second digital images; specifying zones in each of said first and modified second digital images; determining a set of zonal features of each of said specified zones of each of said first and modified second digital images; computing compound mutual information from said first features and said zonal features; altering said modification function; and iterating said transforming, determining, specifying, determining, computing, and altering steps until said compound mutual information is maximized.