Miami ? It’s official: Any value of the World War I-era stamp used to mail in an absentee ballot packet is purely sentimental.

The attention-grabbing “Inverted Jenny” stamp found last month on the envelope of a Florida absentee ballot was declared a fake on Monday.

Representatives from both the Pennsylvania-based American Philatelic Society and the California-based Professional Stamp Experts examined the stamp and agreed it was a copy of the Inverted Jenny, famous for its blue upside-down biplane.

The forged stamp has several differences from a real Inverted Jenny. Mercer Bristow, director of expertizing with APS, measured how many perforations per 2 centimeters the stamp had. A true Inverted Jenny has 11. This one had 10, Bristow said.

The original Jenny stamps were printed in an engraving process. The one on the ballot probably was a lithograph, Bristow said.

Randy Shoemaker, senior expert with PSE, noted that the Jenny was taped on, as if it had no glue. “I think it was a philatelic prank,” he said.

Using a fake stamp is considered revenue fraud. But the case has been reviewed and ruled an isolated incident. It also lacks enough evidence for prosecution, postal inspector Blad Rojo said.