The Presidential Series of stamps from 1938-1943 features a bust side view of each president. Denominations started with 1¢ for Washington, 2¢ for Adams, 3¢ for Jefferson up to 25¢ for McKinley. From there larger denominations of 30¢, 50¢, $1, $2 and $5 were used for Roosevelt, Taft, Wilson, Harding and Coolidge respectively.
Three stamp values ending in 1/2 ¢ featured non-presidents. The 1/2¢ was used for Ben Franklin, 1 1/2¢ was used for Martha Washington, and this stamp of 4 1/2¢ features the only pictorial scene, the White House, home for the president.
From the U.S. Stamp Gallery website:
Since 1800, the White House has been the official residence of the president of the United States. Its address is 1600 Pennsylvania Ave., Washington, DC. James Hoban, an Irish-American architect, was the winner of a 1792 competition for design of the structure. Benjamin Latrobe, principal architect of the Capitol building, sought to improve on the Hoban design as early as 1807. He prepared designs for pavilions at either end, interior alterations, and for porticos on both fronts. Hoban reconstructed the building after it was burned by the British in 1814. He also added the semi-circular South Portico in 1826, which Latrobe had proposed, and three years later completed Latrobe's rectangular North Portico. Extensively remodeled in 1902, additions made at the time were the East Gallery and the Executive Office Wing. Between 1948 and 1952, after the building was pronounced structurally unsound, it was gutted, and its interior structure replaced with steel framing.
From the National Postal Museum website:
The third stamp in the 1938 Presidential Series to feature an image other than that of a president, the 4.5-cent green-gray value depicted the White House. The other two issues not depicting presidents were the Ben Franklin and the Martha Washington.
Inspired by the Leinster House, an Anglo-Irish villa located in Dublin, Irish-born architect James Hoban designed the White House. He won the privilege of designed the presidential mansion in a contest held in 1792 organized by George Washington and Thomas Jefferson. When the structure burned during the War of 1812, Hoban returned to oversee reconstruction. He later added the South and North Porticos.
While it may seem strange that such an unusual denomination—4.5-cent—be included in the Presidential Series, businesses demanded such a rate to pay triple the 1.5-cent third-class per two-ounce merchandise rate (in effect July 1939 through March 1944) and triple the 1.5-cent fourth class book rate at 1.5-cent per pound (in effect November 1938 through June 1942).
The 4.5-cent White House stamp was issued in two varieties—in sheet form (issued July 11, 1938) and in the horizontal (sidewise) coil format (issued January 20, 1939).