The cost of a portrait is often referred to as an investment. A beautiful piece of art, or a family heirloom will become more and more valuable to their owners over time. In instances where people have had to select a few of their treasured items from all of what they own, photographs are the most common possessions chosen, and with good reason.
They are not only difficult or impossible to replace, but more importantly they have the most intrinsic value to their owners.