Art can be any object that has been reclassified and reinterpreted so that they have been imbued with additional value besides usefulness.
A BMW is not just a car. It is a driving experience. It is intelligence. It is status.
A diamond is not just a stone. It is a signal and commitment of one's love.
Human values are commodified into objects, and then bought and sold on a market. Advertising is the process in which this commodification occurs.
Advertisers are artists.