In biometrics terminology, covert or covert environment refers to a biometric sample collection location where individuals in the location are not aware that the sample is being taken. One common covert environment is airport checkpoint security where cameras capture images of travelers that are compared to images on a security watch-list. The image capture and comparison is performed without the traveler's knowledge.
See "Defend Yourself Against Identity Theft" in the "Did You Know..." section of Webopedia.
See also "How Biometrics Security Works" in the "Did You Know..." section of Webopedia.
Also see "How Fingerprint Scanners Work" in the "Did You Know..." section of Webopedia.