1. A computer-implemented passive continuous authentication method, comprising the steps of: registering at least one facial image of a user into a user image database; iteratively determining, during the registering step, a set of weighting masks associated with the user's at least one facial image stored in the user image database, the weighting masks being optimized by applying an interactive artificial bee colony optimization procedure to raw data of the user's at least one facial image stored in the user image database, the interactive artificial bee colony optimization procedure having a fitness function that seeks to minimize within cluster distances and between cluster distances of the raw facial image data during the optimization procedure, the iteratively determining step continuing until a stopping criterion is reached; allowing a registered user in the user image database to log into and use a computing resource; continuously authenticating, in real time, captured image frames in the vicinity of the computing resource against the user's registered at least one facial image in the image database, the continuously authenticating step including: determining Eigenface values associated with the real-time captured image frames; applying the optimized weighting masks to the Eigenface values, thereby providing processed real-time captured image frames; and comparing the processed captured image frames to the user's registered at least one image; continuing to allow use of the computing resource so long as there is a match between the processed captured image frames and the user's registered at least one facial image in the image database; and disallowing use of the computing resource when there is a mismatch between the processed captured image frames and the user's registered at least one facial image in the image database.