Great Britan, 1873
*UPDATE: reader Ian corrects us! These photographs of Sir Isaac Pitman, Vice President of the Vegetarian Society may have been taken prior to 1873.
Originally, I thought this could be the earliest photograph of a vegetarian. A little piece of man-veg history:
Francis William Newman, Carte-de-visite Photograph, by The London Stereoscopic & Photographic Company, London.
President of the Vegetarian Society of Great Britain from 1873-84
Joshua Katcher