Paintings

Paintings are non-craftable Decorative Furniture. There are currently 70 obtainable paintings, of which 14 are sold by the Painter under certain circumstances, 15 are found in underground cabins, 22 are found in the Dungeon, 13 are found in the Underworld, 5 can be gotten from Goodie Bags, and 1 can be obtained from the Angler as a quest reward.

From Painter
Paintings purchased from the Painter bear the tooltip "V. Costa Moura", apparently the artist's name.

Trivia
(V. Costa Moura > Costa Moura > Cost Mour > Cost more)
 * The paintings that are "attributed" to V. Costa Moura could mean that they are worth less than what they are sold for.
 * They could also be a reference to the fact that items are bought at 5x the sell price. (V = 5, Costa Moura stated above)