When most of us say we want an “appraisal” on a work of art we are basically just asking for an opinion on its worth, thank you Antiques Road Show. That is a very generic use of the term “appraisal”.
In reality, since the Savings and Loan debacle back in the 1980’s, the term “Appraisal” for both real and personal property now has very legal meanings and there are existing standards for appraisals governed by law.
If you need an appraisal of a work of art for legal reasons, tax or estate purposes, donation to a museum or not-for-profit, damages, liquidation or bankruptcy there are now USPAP standards for those appraisals and your appraiser needs to have passed the USPAP test and write the appraisal to those standards using the correct forms and terms. (All insurance companies are different and have different requirements so you need to check with your carrier to find out what type of appraisal they will accept for insurance purposes.)
The Appraisers Association of America 386 Park Avenue South, Suite 2000, New York, NY 10016 212.889.5404 is who you want to contact for art appraisals. Other national groups specialize in real estate appraisals.