When does intellectual property statue of limitations run out? When the event happens or when the artist finds out about it?

Unpermitted copying of a work of the graphic arts is covered by the law of copyright. As a general matter, the statute of limitations for copyright infringement is three years from the date when the infringement reasonably should have been discovered, which will be a very difficult showing under circumstances such as you suggest. Please call my office at (203) 399-1320 if you wish to discuss this situation.