Attorneys for the Andy Warhol Foundation for the Visual Arts on Tuesday urged a federal appeals court to uphold a lower court’s finding that the iconic artist made “fair use” of a 1981 photograph of Prince when he created a series of silkscreen images of the musician decades ago.

The argument, which aims to protect potentially thousands of Warhol works from copyright infringement challenges, centered on whether U.S. District Judge John G. Koeltl of the Southern District of New York applied the correct legal test in ruling for the foundation last July.