http://www.copyright.cornell.edu/tra...lic_Domain.htm
The link above is to a site that has a pretty good chart of what's in the public domain and what's not. To be safe, photograph items that are generic. For instance, an ordinary basketball is fine. But one with the brand name on it would be something I'd avoid.
Antiques are, for the most part, a safe bet. Be careful of antiques with trademarked images. It's not unusual for an image to be in the public domain in terms of copyright but to be trademarked.
Kathryn