There are many types of value involved with art. Aesthetic value is simply the value the viewer gives the piece- if you enjoy a work of art, then you give it high value. Monetary value is often concerned with the age of the work and the artist who created it.
Value is how bright things are or, in another way, how much grey tones they have behind the initial colors. A black and white photograph shows a large range of value, for example, from all the different grays.
