What constitutes a conviction of possession of a firearm?

Title 18 U.S.C. 922(g)(1) prohibits possession of a firearm by any person ... who has been convicted in any court of, a crime punishable by imprisonment for a term exceeding one year. What constitutes a conviction of such a crime shall be determined in accordance with the law of the jurisdiction in which the proceedings were held. 18 U.S.C. 921(a)(20); accord United States v. Valerio, 441 F.3d 837, 839 (9th Cir.2006) (Under the federal felon in possession statute, state law controls on whether a person has a conviction,....).