Once you’ve determined exactly what you have along with provenance and its value you’ll want to ensure both that the artwork has never been stolen, and that, should it be stolen in the future, you’ll have the best possible chance of recovering it.
The Art Loss Register holds the world’s largest private database of lost, stolen and looted art, antiques and collectibles, currently listing more than 700,000 items. Subscription and search services offered.
Federal Bureau of Investigation: Art Theft
This is the site for the National Stolen Art File.
The AAM Guide to Provenance Research by Nancy H. Yeide. Washington, D.C.: American Association of Museums, c2001. N3999.Y45 2001 AH/C Reference. Guide for tracing the ownership history of works of art. Focused on cultural property looted by the Nazis and others during WWII, it is divided into three parts: Basic Provenance Research and Principles; Holocaust-Era Provenance Research; and Appendixes, which include bibliographies of collections, dealer archives, and “red flag names” compiled by the Office of Strategic Services.
by Robin Thornes, with contributions by Peter Dorrell and Henry Lie, 1999
Object ID: An international standard for describing art, antiques and antiquities
Object Identification (Object ID) is an international standard used for describing cultural objects, facilitating the identification of collections of archaeological, cultural and artistic objects in case of loss or theft. It sets a standardized procedure to document and describe these objects.
Provenance Guide by The International Foundation for Art Research (IFAR)
Stolen Art Alert Publication and Art Theft Archive Newsletter by The International Foundation for Art Research (IFAR)