Gordon
The paintings (I think there were at least two, right?) that remind Lightsong of his dreams and the Manywar etc. Is the Artist someone we know? If not, will we eventually meet him/her in a later book? Does the artist hope to affect Lightsong this way, or is it just some guy giving abstract art to his God?
Jared
Is the artist that painted those paintings Hoid?
Brandon Sanderson
Hoid did not make the paintings. The goal of those paintings—and this is spoilery, by the way—the paintings are actually what the text implies that they are. They are abstract paintings which Lightsong, having a touch of the divine, is able to see and read into things that aren't necessarily there.
Beyond that, art is a magical thing in the world of WARBREAKER. When an artist creates a work of art, part of the artist's soul ends up in the artwork. Someone who has many breaths and who's Returned like Lightsong has the inherent ability to see into the art and perceive that. So Lightsong can interpret correctly an abstract piece, based on what the artist is trying to convey, in a way that a normal person couldn't.
I was not trying to make the artists anyone specifically important. In the case of those paintings, they are wonderful artists—I think they are two separate artists, if I'm thinking of the two paintings that you're indicating. As Lightsong has a splinter of divine nature inside him, he is able to interpret the paintings—to foresee, using them, and to see into the soul of the person who made them.