An Post has stopped the printing of a new stamp commemorating Captain Jack White, one of the founders of the Irish Citizen Army, amid doubts over its authenticity.

The 60 cent stamp, issued this morning, features a black and white photograph of about 20 uniformed volunteers headed by a mustachioed man identified as Cpt White.

However, several historians have contacted An Post to tell them they have the wrong man. The man in the photograph has yet to be identified and An Post has removed publicity information about the stamp from its website.

A spokeswoman for the company said it was deferring issuing the stamp until the matter has been resolved.

“This image, which was researched and verified, has been widely used over the years in academic journals and other publications. However, following advance publicity for the stamp yesterday, a number of historians have disputed the veracity of the image, saying the man depicted is not Jack White.”

Cpt White formed the ICA along with James Larkin and James Connolly during the 1913 Lockout to protect trade unionists from the violent tactics used by the Dublin Metropolitan Police to break up demonstrations.