A forensic authentication system includes an imaging device to capture an image of a printed mark and a non-printed area of a substrate directly adjacent to the printed mark, and a processor to run computer readable instructions. The processor can run computer readable instructions to utilize a model to define a substrate region that corresponds with at least a portion of the non-printed area of the substrate directly adjacent to the printed mark; and computer readable instructions to generate a substrate signature for the defined substrate region. Each of the computer readable instructions is embedded on a non-transitory, tangible computer readable medium.