Cal. Penal Code § 290.016

(a) On or after January 1, 1998, upon incarceration, placement, or commitment, or prior to release on probation, any person who is required to register under the Act shall preregister. The preregistering official shall be the admitting officer at the place of incarceration, placement, or commitment, or the probation officer if the person is to be released on probation. The preregistration shall consist of all of the following:
1. (1) A preregistration statement in writing, signed by the person, giving information that shall be required by the Department of Justice.
2. (2) The fingerprints and a current photograph of the person.
3. (3) Any person who is preregistered pursuant to this subdivision is required to be preregistered only once.
(b) Within three days thereafter, the preregistering official shall forward the statement, fingerprints, photograph, and vehicle license plate number, if any, to the Department of Justice.