1. A method for detecting scalp or facial hair of a human subject depicted in a digital image and implemented at least in part by a computer system, the method comprising the steps of: obtaining a digital image from a digital image-record collection; linking the digital image to a variable amount of image metadata including semantic information relating to the content of the image and structural information relating to conditions under which the image was captured; identifying (a) gender information indicating a gender of the human subject, (b) age information indicating an age or approximate age of the human subject, or (c) hair characteristic information indicating a set of hair characteristics associated with the human subject; identifying an expected-hair region within the digital image based at least upon the identified information, the expected-hair region inclusive of at least a portion of a head to the human subject; identifying a hair region within the expected hair region; and using the information pertaining to the identified hair region with at least one of a computer software program and a computer-accessible memory to provide various functional outputs relative to the digital image.