What is the difference between screening and covert screening?

What will be an ideal response?

Screening involves a reasonable examination of persons, cargo, vehicles, or baggage for the protection of the vessel, its passengers, and crew. Covert screening occurs in situations where biometric samples are being collected at a location that is not known to bystanders. An example of a covert environment might involve an airport checkpoint where face images of passengers are captured and compared to a watch list without passengers' knowledge.