passports or group passports. A passport application could cover, variously, a wife, a child, or children, one or more servants, or a woman traveling under the protection of a man. The passport would be issued to the man. Similarly, a passport application could cover a child traveling with their mother. The passport would be issued to the mother. The number of Americans who traveled without passports is unknown. The League of Nations held a conference in 1920 concerning passports and through-train travel, and conferences in 1926 and 1927 concerning passports. The 1920 conference put forward guidelines on the layout and features of passports, which the 1926 and 1927 conferences followed up. Those guidelines were steps in the shaping of contemporary passports. One of the guidelines was about 32-page passport booklets, such as the U.S. type III mentioned in this section, below. Another guideline was about languages in passports. A conference on travel and tourism held by the United Nations in 1963 did not result in standardized passports. Passport standardization was accomplished in 1980 under the auspices of the International Civil Aviation Organization. The design and contents of U.S. passports changed over the years. Prior to World War I the passport was typically a large () diploma, with a large engraved seal of the Department of State at the top, repeated in red wax at the bottom, the bearer's description and signature on the left, and his name on the right above space for data such as "accompanied by his wife," all in ornate script. In 1926, the Department of State introduced the type III passport. This had a stiff red cover, with a window cut-out through which the passport number was visible. That style of passport contained 32 pages. American passports had green covers from 1941 until 1976, when the cover was changed to blue, as part of the U.S. bicentennial celebration of 1975–1977, and remained blue afterwards until 1993. Green covers were again issued from April 1993 until March 1994, and included a special tribute to Benjamin Franklin in commemoration of the 200th anniversary of the United States Consular Service. After March 1994, blue passports, with pages showing U.S. state seals, were reissued. In 2007, images showcasing landscapes of the United States as well as places and objects of significance to U.S. history were introduced. Initially, a U.S. passport was issued for two years, although by the 1950s on