People have asked about the background picture in the poster's montage:

This is a famous painting by the early American artist Erastus Salisbury Field (1805-1900). He titled his 9 x 13 foot canvas, which is now on display at the Museum of Fine Art, Springfield, Massachusetts, "The Historical Monument of the American Republic." Field's grandiose vision of a monument, which predated the first skyscraper, is covered with panels, sculptures, and carvings depicting important figures, events, and documents in our nation's history, and standing along the top of its towers are rows of angels, many holding the American flag.

Read this ARTICLE on the Springfield Library and Museums Association website.