I know a lot about black & white printing processes, color printing, and color transparencies. This sort of thing, not so much. I think, and I encourage anyone who can either verify or contradict that opinion to do so, that this is a rotogravure. I'm also going on guess work as to the source of this image. Marked "U.S. OFFICIAL" and "SIGNAL CORPS U.S.A." on the front, it is my opinion that these are press release photos used to publicize the first world war. President Woodrow Wilson was so committed to a total war effort, that even the press was conscripted into the fight. Captioned "French tanks ("Chars d"Assault") moving to the support of French troops operating on the left of the 32d Div., Aug.29, 1918."