(a) Any person who advertises for sale or distribution any obscene matter knowing that it depicts a person under the age of 18 years personally engaging in or personally simulating sexual conduct, as defined in Section 311.4, is guilty of a felony and is punishable by imprisonment in the state prison for two, three, or four years, or in a county jail not exceeding one year, or by a fine not exceeding fifty thousand dollars ($50,000), or by both such fine and imprisonment.
(b) Subdivision (a) shall not apply to the activities of law enforcement and prosecution agencies in the investigation and prosecution of criminal offenses.