The plain view doctrine is a creature of the common law.
In the United States, the plain view doctrine was defined by the Supreme Court of the United States in Texas v. Brown as requiring lawful intrusion, discovery of the evidence inadvertently, and that it be immediately apparent that the object may be evidence of a crime, contraband, or otherwise subject to seizure.
In US v Smith, Justice Gerald Tjoflat of the United States Court of Appeals adopted these words:
"The plain view doctrine permits a warrantless seizure where (1) an officer is lawfully located in the place from which the seized object could be plainly viewed and must have a lawful right of access to the object itself; and (2) the incriminating character of the item is immediately apparent.
"The plain view doctrine allows police officers to seize any contraband in plain view if the officers have a right of access to the place where the contraband is located.
"An example of the applicability of the plain view doctrine is the situation in which the police have a warrant to search a given area for specified objects, and in the course of the search come across some other article of incriminating character. The officers, however, must have probable cause to believe that the object in plain view is contraband. If the police lack probable cause to believe that an object in plain view is contraband without conducting some further search of the object — i.e., if its incriminating."
In Canada, §489(2) of the Criminal Code (2011) codifies the plain view doctrine:
"Every peace officer…who is…present in a place ... in the execution of duties may, without a warrant, seize any thing that the officer believes on reasonable grounds will afford evidence in respect to an offence."
In R v Splindoe, Justice Jackson of the Saskatchewan Court of Appeal used these words in her judgment:
"Plain view occurs when evidence falls into the view of an officer who has a right to be in the position he is in to have the view he has had; such items have been held to be subject to seizure....
"The plain view doctrine may not be used to extend a general exploratory search from one object to another until something incriminating at last emerges.
The plain view doctrine confers a seizure power not a search power. It does not permit an exploratory search to find other evidence."
In R v Fawthrop, Justice Borins wrote:
"The test in applying the plain view doctrine to justify a seizure of evidence is not whether the police would have found the items in plain view while searching for the photographs as the trial judge believed, but whether they did find the items in plain view while executing a valid warrant or while lawfully present in the appellant's residence."
An example would be the seizure of marijuana plants in plain view of a police officer otherwise at the door of a private residence; or the discovery of a machine gun in the back seat of a car pulled over for a drunk driving road test.