In a section about the famous photo of Harry Truman holding up the 'Truman Defeats Dewey' paper, McCullough writes: "Like some other photographs of other presidents - of Theodore Roosevelt in a white linen suit at the controls of a steam shovel in Panama, or Woodrow Wilson at Versailles...this of Harry Truman in 1947 would convey the spirit of both the man and the moment as almost nothing else would."
I'm going to make a guess that McCulloch is referring to this photo of the "Big Four" at Versailles (from left to right: UK Prime Minister David Lloyd George, Italian Prime Minister Vittorio Orlando, French Premier Georges Clemenceau, and Wilson).
The photo was taken by Captain Edward Jackson, and accompanying newsreel footage was filmed by Lieutenant Viktor Kubes, both of the US Army Signal Corps. Jackson was a photographer for Hearst's newspapers before and after the war, and during the Versailles conference was an official photographer for the US delegation. Apparently Jackson recounted the photo shoot to American Legion Weekly in 1922, and a scan of that can be found here. It's a very interesting and entertaining read. Jackson took a photo portrait indoors, but also wanted to take one outside for better lighting. Lloyd George was very enthusiastic for the photos, Wilson was neutral, and Clemenceau was incredibly grumpy.