They disintegrate, change, crack, and fall off and break. On famous works of art, before and after photos don t always appear to be the same piece. There are unfortunately no standards for art authenticity within the art market. Some insurance companies require an appraisal. Some insurance companies require authenticity.
Some insurance companies require neither.
Some insurance companies require both. None have a standard regarding degree of authenticity or accepted experts. When it comes to establishing value, some accept invoices, some accept appraisals by dealers, and some require independent appraisals. In litigation, regarding Fine Art, whether it s divorce, probate, fraud, etc. It is usually non-scientific and therefore one person s opinion against another.