The moment an image is created by an artist, the artist holds and owns the copyright. When a work of art is sold whether an exisiting piece or commissioned work for a private collector, the purchaser is the owner of the actual piece. The copyright on the sold work remains with its creator, the artist. The artist owns the copyright and as such is the only one who can reproduce the image.
Business and Corporate collectors:
The exception to this is when the copyright is sold along with the original painting. This would be a beneficial arrangement for private Business and Corporate Commissions. This is more costly but gives the purchaser the freedom to use the image for marketing purposes etc..There must be a full written signed agreement between the artist and the purchaser releasing pre-determined rights to the buyer. This situation has proven to be a financial plus for many business organizations.