Paper money in the U. S. wasn’t printed by the Federal Government until the civil war. Prior to the war, paper money was printed and backed by private banks (hence the term Bank Notes).
Green ink was used on the back of bills as an early anti-counterfeit tactic as it was hard to reproduce. This is where the term “greenbacks” comes from.
Here is an example of one of the earliest U.S. currencies - a 1776 five shilling note. It was printed by John Adams, - notice the warning on the back of the bill - “To Counterfeit Is Death”.
Early U.S. money had some odd values. Here is a 2/3’s dollar
And, an early $1.50 bill
During the Civil War period, the Bureau of Engraving and Printing printed paper notes in denominations of 3 cents, 5 cents, 10 cents, 25 cents, and 50 cents. The reason for this is that during the Civil War, people hoarded coins because of their intrinsic value which created a drastic shortage of circulating coins.
During this war, the rebel states also produced their own currency. Early on in the war, the notes were accepted, and held their value, but as the South began to lose, the value plunged until they became all but worthless. Towards the end of the war, Northern money was being smuggled in to pay the Southern soldiers. Ironically, the value of these bills has risen again as the bills became collectors items.
Historically, most bills have shown the image of only a single historical figure on the front side. This unusual bill carried six different people.