1. A method for registering first and second digital images captured using first and second different capture modalities, said method comprising the steps of: transforming said second digital image in the second modality to be more like said first digital image in the first modality 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 mutually exclusive zones in each of said first and modified second digital images where each of the specified mutually exclusive zones is less than an entirety of each of said first and modified second digital images; determining a set of zonal features of each of said specified mutually exclusive zones of each of said first and modified second digital images; computing compound mutual information from said first features and said zonal features where compound mutual information comprises an aggregate measure of mutual information; altering said modification function; and iterating said transforming, determining, specifying, determining, computing, and altering steps until said compound mutual information is maximized, wherein said computing further comprises: (1) extracting a set of global marginal densities from a set of global features and a set of zonal marginal densities from said set of zonal features, and (2) applying weighting coefficients to said sets of marginal densities to provided weighted marginal mutual information, and aggregating said weighted marginal mutual information in accordance with the formula: I ⁡ ( A , B ) = ∑ m = 1 M ⁢ ⁢ ( λ m ⁢ ∑ h a ⁢ h b ⁢ ⁢ ( p ⁡ ( h a m , h b m ) ⁢ log ⁢ p ⁡ ( h a m , h b m ) p ⁡ ( h a m ) ⁢ p ⁡ ( h b m ) ) ) where A and a signify the first digital image; B and b signify the modified second digital image; M is the total number of sets of global and zonal features; p(h a m ), p(h b m ) and p(h a m , h b m ) are marginal densities derived from image features {h m } m=1 M ; and λ m are weighting coefficients, where ∑ m ⁢ ⁢ λ m = 1.