Counterfeiting dollars from images on the Net is a growing problem
Experts say the 'greenback' is so easy to forge from images on the Net that teenagers are printing them at home on their computers.
Anyone with one of the latest ink-jet printer can produce a reasonable copy.
Recently, a 16-year-old New Yorker was arrested when he tried to buy bubblegum with a home-made $10 bill.
The US Treasury has calculated that more than 4% of the forged notes currently in circulation are created on computers.
It is calling for longer sentences to be imposed on the forgers to dissuade them from perfecting their art.
It is illegal to make colour, small-size copies of US notes.
They may, however, be copied in black and white and must be larger than 150% of the note size or less than 75% of the note size.
European notes are less easy to counterfeit because they have a more colourful and complicated design.
The Bank of England admits that there is a small number of forged notes circulating in the British economy but says few counterfeits are good enough to pass four simple tests.
They recommend that anyone who thinks they may have been given a forged note to first of all feel the paper.
Special printing processes on genuine money produces a unique feel. It should be crisp, not limp or waxy and some of the lettering will feel rough to the touch.
The watermark of a clearly defined portrait of the Queen should be visible when the note is held up to the light.
It is important to look at the quality of the printing to make sure the lines are sharp and well-defined and that the colours are clear and distinct.
Suspicious shoppers or shop owners should also check the metallic thread which runs through the note as a series of silver dashes.
If it is held up to the light the thread shows up as a bold, continuous line.
The £50 note introduced in 1994 also has an additional security feature - a silver reflective rose and medallion.