When I saw this last night I naturally assumed that it was Photoshopped (so many cool pictures turn out to be these days) but it's totally legit:
The design for the living picture was laid out at the drill ground at Camp Dodge, situated in the beautiful valley of the Des Moines River. Thousands of yards of white tape were fastened to the ground and formed the outlines on which 18,000 officers and men marched to their respective positions.It was taken in 1918 and was intended to promote war bonds but it was never used. You can see other similar "people pictures" from the same time period at the Carl Hammer Gallery here.
The day on which the photograph was taken was extremely hot and the heat was intensified by the mass formation of men. The dimensions of the platting for the picture seem astonishing. The camera was placed on a high tower. From the position nearest the camera occupied by Colonel Newman and his staff, to the last man at the top of the torch as platted on the ground was 1,235 feet, or approximately a quarter of a mile...
Incredible as it may seem there are twice the number of men in the flame of the torch as in the whole remaining design, while there are eight times as many men in the arm, torch and flame as in all the rest of the figure. It will be noted that the right thumb is five feet longer than the left hand, while the right arm, torch and flame is eight times the length of the body.