1. A differential wavelength imaging method for detection and identification of concealed materials comprising: (a) capturing a plurality of sample images of a target at two or more key NIR wavelengths or bands of wavelengths; (b) producing a differential wavelength image of the target based on the sample images, the differential wavelength image comprised of a plurality of pixels having a pixel value based on intensity; (c) compiling a plurality of differential wavelength image pixel values associated with the sample images to produce total processed image data, and evaluating the total processed image data so as to identify pixels within the differential wavelength image having a higher or lower intensity value than surrounding covering materials; and (d) comparing the intensity values of the pixels having a higher or lower intensity value than the covering materials with NIR reflection spectra of known contraband materials to determine correspondence therewith, so as to identify the concealed material(s) associated with the pixels having a higher or lower intensity value than the covering materials.