BOSTON (AP) — The U.S. Postal Service has unveiled a new stamp to mark the 100th anniversary of President John F. Kennedy's birth.

The Forever stamp was released Monday during the annual Presidents Day family festival at the John F. Kennedy Presidential Library in Boston.

Among those attending were Kennedy family members, including U.S. Rep. Joe Kennedy of Massachusetts, the grandson of Robert F. Kennedy.

He told a standing-room-only crowd that the stamp, which features a 1960 photograph of John F. Kennedy with his eyes tilted upward, showed his great-uncle's perpetual optimism and confidence.

The stamp will be on sale in U.S. post offices starting Tuesday.

The future president was born in Brookline on May 29, 1917, the second of Joseph and Rose Fitzgerald Kennedy's nine children.