The Old Executive Office Building around 1909. Image courtesy of the Library of Congress, National Photo Company Collection.
Originally built as the State, War, and Navy Building, and completed in 1888, it remains much the same as it was around 1909, despite having changed its function. Today, it is used by various executive departments, including the Office of the Vice President, as it is located directly adjacent to the White House (the white house is immediately to the left of the photos)
However, probably the most unusual thing in either photo is the presence of a cow in the 1909 photo. It is, in fact, a real cow, and was actually kept for agricultural purposes by none other than William Howard Taft. In the days before refrigeration, the best way to ensure an ample supply of fresh milk was by actually keeping a cow on the White House grounds. Named Pauline Wayne, the cow provided milk for the Taft family for about a year and a half, and was the last cow to reside at the White House [insert joke about President Taft’s weight here].