Thomas Jefferson, the tallest standing figure, lays the draft declaration on the table at the center of the painting. Trumbull painted a study of Jefferson from life while he lodged with the U.S. envoy to Paris in 1785. According to Wikipedia:
John Trumbull‘s Declaration of Independence is a 12-by-18-foot oil-on-canvas painting in the United States Capitol Rotunda that depicts the presentation of the draft of the Declaration of Independence to Congress. It was based on a much smaller version of the same scene, presently held by the Yale University Art Gallery. Trumbull painted many of the figures in the picture from life and visited Independence Hall as well to depict the chamber where the Second Continental Congress met. The oil-on-canvas work was commissioned in 1817, purchased in 1819, and placed in the rotunda in 1826.
The painting is often described as the “Signing of the Declaration of Independence”, but this is an error. The painting actually shows the five-man drafting committee presenting their draft, an event that took place on June 28, 1776, and not the signing of the document, which took place later.
The painting shows 42 of the 56 signers of the Declaration; Trumbull originally intended to include all 56 signers, but was unable to obtain likenesses for all of them. He also decided to depict several participants in the debate who did not sign the document, including John Dickinson, who declined to sign. Because the Declaration was debated and signed over a period of time when membership in Congress changed, the men in the painting had never all been in the same room at the same time.
Thomas Jefferson seems to be stepping on the foot of John Adams in the painting, which many think is supposed to symbolize their relationship as political enemies. However, upon closer examination of the painting, it can be seen that their feet are merely close together.