An underwater image area is illuminated with light generating elastic scattering from manmade objects and naturally-occurring features, and fluorescence from naturally-occurring features. Local standard deviation (LSD) images are formed using the elastic scattered and fluorescent light. Elements of each LSD image are compared to threshold criteria to generate: i) first binary images having first image state portions indicating manmade objects and naturally-occurring features, and ii) second image state portions indicating background. The first binary images are logically combined generating a composite image mask. Statistical threshold criteria for each fluorescence-based image is generated using only portions identified by portions of the composite image mask indicating of background. Elements of each fluorescence-based image are compared to statistical threshold criteria to generate second binary images. At least two second binary images are logically combined to generate a binary manmade object image mask delineates between manmade objects and everything else.