A painting hangs on the wall or lies flat in storage. It rarely fits in a small certified safe, and a tight steel box is often too dry for canvas and too hot in a fire. In the overview Security for collectors, this is the case where the room is the protection and the folder holds the price.
What breaks without a thief
Direct light bleaches. Damp warps, dryness cracks. A heater under the frame works every winter. You do not hang the expensive sheet above the heater, and not in the south window. You take condition photos once, in good light: the front, and details of damage that is already there.
When someone comes
The big documented picture thefts sit in museums. For the home, what applies is this: visible on the wall toward the street, and the door that an ordinary burglary opens. An alarm, unobtrusive hanging, no inventory on the web. What is small enough for a portfolio can go in the fire-resistant cabinet, if the climate there is right. The large canvas stays in place, and the policy knows it individually.
The folder
Artist, title, dimensions, technique, provenance, proof, condition photo. Insurance as a named item, not as "art in the household contents". The guide on insurance says where the flat sum ends.