Possible Clues:

• Pictures on Father's Day cards?
• Works with everyday objects
• Warhol's output
• Andy Warhol's works
• Lichtenstein movement
• Striking pictures of everyday things in region without work
• Work in section producing comic strips
• Certain 1960's paintings
• Dad finds a right time to view Andy Warhol's work
• Work done by Warhol's secretary in New York, say