I'm am artist and I sell my original paintings. 
The person who buys the painting owns just the 
painting. As the artist I retain the copyright 
and therefore am the only one who has the legal 
right to reproduce that image on cards, posters, 
etc. I can sell the copyright also, seperate from 
the painting but most artists don't, they just 
sell the artwork and keep the copyright. Hope 
that helps.